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 :-)

libdevcore/Base64.h

@@ -0,0 +1,42 @@
+/*
+   base64.cpp and base64.h
+
+   Copyright (C) 2004-2008 René Nyffenegger
+
+   This source code is provided 'as-is', without any express or implied
+   warranty. In no event will the author be held liable for any damages
+   arising from the use of this software.
+
+   Permission is granted to anyone to use this software for any purpose,
+   including commercial applications, and to alter it and redistribute it
+   freely, subject to the following restrictions:
+
+   1. The origin of this source code must not be misrepresented; you must not
+	  claim that you wrote the original source code. If you use this source code
+	  in a product, an acknowledgment in the product documentation would be
+	  appreciated but is not required.
+
+   2. Altered source versions must be plainly marked as such, and must not be
+	  misrepresented as being the original source code.
+
+   3. This notice may not be removed or altered from any source distribution.
+
+   René Nyffenegger rene.nyffenegger@adp-gmbh.ch
+*/
+/// Adapted from code found on http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c
+/// Originally by René Nyffenegger.
+/// DEVified by Gav Wood.
+#pragma once
+
+#include <string>
+#include "Common.h"
+#include "FixedHash.h"
+
+namespace dev
+{
+
+std::string toBase64(bytesConstRef _in);
+bytes fromBase64(std::string const& _in);
+
+
+}