Documentation Structure Change and Cleanup (#2808)

* Update docs/sdk/clients.md
* organize ADR directory like tendermint
* docs: move spec-proposals into spec/
* remove lotion, moved to website repo
* move getting-started to cosmos-hub, and voyager to website
* docs: move lite/ into clients/lite/
* move introduction/ content to website repo
* move resources/ content to website repo
* mv sdk/clients.md to clients/clients.md
* mv validators to cosmos-hub/validators
* move deprecated sdk/ content to _attic
* sdk/modules.md is duplicate with modules/README.md
* consolidate remianing sdk/ files into a single sdk.md
* move examples/ to docs/examples/
* mv docs/cosmos-hub to docs/gaia
* Add keys/accounts section to localnet docs

docs/reference/baseapp.md

@@ -0,0 +1,14 @@
+# baseApp
+
+`baseApp` requires stores to be mounted via capabilities keys - handlers can only access stores they're given the key to. The `baseApp` ensures all stores are properly loaded, cached, and committed. One mounted store is considered the "main" - it holds the latest block header, from which we can find and load the most recent state.
+
+`baseApp` distinguishes between two handler types - the `AnteHandler` and the `MsgHandler`. The former is a global validity check (checking nonces, sigs and sufficient balances to pay fees,
+e.g. things that apply to all transaction from all modules), the later is the full state transition function.
+During CheckTx the state transition function is only applied to the checkTxState and should return
+before any expensive state transitions are run (this is up to each developer). It also needs to return the estimated
+gas cost.
+
+During DeliverTx the state transition function is applied to the blockchain state and the transactions
+need to be fully executed.
+
+BaseApp is responsible for managing the context passed into handlers - it makes the block header available and provides the right stores for CheckTx and DeliverTx. BaseApp is completely agnostic to serialization formats.