Make the Solidity repository standalone.

This commit is the culmination of several months of work to decouple Solidity from the webthree-umbrella so that it can be developed in parallel with cpp-ethereum (the Ethereum C++ runtime) and so that even for the Solidity unit-tests there is no hard-dependency onto the C++ runtime.

The Tests-over-IPC refactoring was a major step in the same process which was already committed.

This commit contains the following changes:

- A subset of the CMake functionality in webthree-helpers was extracted and tailored for Solidity into ./cmake.   Further cleanup is certainly possible.
- A subset of the libdevcore functionality in libweb3core was extracted and tailored for Solidity into ./libdevcore.   Further cleanup is certainly possible
- The gas price constants in EVMSchedule were orphaned into libevmasm.
- Some other refactorings and cleanups were made to sever unnecessary EVM dependencies in the Solidity unit-tests.
- TravisCI and Appveyor support was added, covering builds and running of the unit-tests (Linux and macOS only for now)
- A bug-fix was made to get the Tests-over-IPC running on macOS.
- There are still reliability issues in the unit-tests, which need immediate attention.    The Travis build has been flipped to run the unit-tests 5 times, to try to flush these out.
- The Emscripten automation which was previously in webthree-umbrella was merged into the TravisCI automation here.
- The development ZIP deployment step has been commented out, but we will want to read that ONLY for release branch.

Further iteration on these changes will definitely be needed, but I feel these have got to sufficient maturity than holding them back further isn't winning us anything.    It is go time :-)

cmake/FindPackageMessage.cmake

@@ -0,0 +1,57 @@
+#.rst:
+# FindPackageMessage
+# ------------------
+#
+#
+#
+# FIND_PACKAGE_MESSAGE(<name> "message for user" "find result details")
+#
+# This macro is intended to be used in FindXXX.cmake modules files.  It
+# will print a message once for each unique find result.  This is useful
+# for telling the user where a package was found.  The first argument
+# specifies the name (XXX) of the package.  The second argument
+# specifies the message to display.  The third argument lists details
+# about the find result so that if they change the message will be
+# displayed again.  The macro also obeys the QUIET argument to the
+# find_package command.
+#
+# Example:
+#
+# ::
+#
+#   if(X11_FOUND)
+#     FIND_PACKAGE_MESSAGE(X11 "Found X11: ${X11_X11_LIB}"
+#       "[${X11_X11_LIB}][${X11_INCLUDE_DIR}]")
+#   else()
+#    ...
+#   endif()
+
+#=============================================================================
+# Copyright 2008-2009 Kitware, Inc.
+#
+# Distributed under the OSI-approved BSD License (the "License");
+# see accompanying file Copyright.txt for details.
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+# (To distribute this file outside of CMake, substitute the full
+#  License text for the above reference.)
+
+function(FIND_PACKAGE_MESSAGE pkg msg details)
+  # Avoid printing a message repeatedly for the same find result.
+  if(NOT ${pkg}_FIND_QUIETLY)
+    string(REPLACE "\n" "" details "${details}")
+    set(DETAILS_VAR FIND_PACKAGE_MESSAGE_DETAILS_${pkg})
+    if(NOT "${details}" STREQUAL "${${DETAILS_VAR}}")
+      # The message has not yet been printed.
+      message(STATUS "${msg}")
+
+      # Save the find details in the cache to avoid printing the same
+      # message again.
+      set("${DETAILS_VAR}" "${details}"
+        CACHE INTERNAL "Details about finding ${pkg}")
+    endif()
+  endif()
+endfunction()