Mock Application For LCD / move lcd tests to modules

[rigelrozanski]

Similarly to how the module-specific application-level tests for transactions formerly in cmd/gaia/app/app_test.go where moved into their respective modules through the use of a mock application - The LCD tests currently housed in client/lcd/lcd_test.go should be moved into their respective module packages.

This also means restructuring client/lcd/test_helpers.go to not import the cmd/gaia/app and instead allowing each module-lcd test to define its own mock application to test within.

Ideally we can simple adapt the existing mock application framework used for app_tests to satisfy use in the lcd tests as well.

checkout the app_test: https://github.com/cosmos/cosmos-sdk/blob/develop/x/stake/app_test.go
checkout the existing mock framework: https://github.com/cosmos/cosmos-sdk/tree/develop/x/mock

CC: @adrianbrink @dev @alexanderbez

[fedekunze]

@rigelrozanski Will move staking LCD tests to the stake module with #1880

[rigelrozanski]

@fedekunze you should sync with @ebuchman if you are going to be making any radical changes - ALSO I kind of think we should either do it for ALL of the lcd tests simultaneously or just hold-off - I don't want a disjointed code base, I think that gets confusing

[fedekunze]

Ok, makes sense

[fedekunze]

Closing as we now have contract tests