app: added getPlatform function, and ErrInvalidPlatform variable
app: move platform tests to their own suite
app: validate app platform on CreateApp

This is a backward compability break...
app: change struct field

I'm keeping it compatible with the current database.
cmd/tsuru-admin: version 0.1.6
cmd/tsuru: version 0.7.10
cmd/tsuru: use platform instead of framework in app-create

Ops, that was broken...
api: multiple fixes related to recent platform change

1. Receive "platform" in createApp handler
2. Fix all tests that call app.CreateApp
cmd: fix version validation code

It used string comparation, so 0.10 was smaller than 0.2.
api: request tsuru version 0.7.9

It should be 0.7.10, but it won't work because of the bug fixed by
73a36ce9b7fb838e6aacf2fc758c5324db9d38eb.

Next releases will work fine :-)
cmd/tsuru: remove unnecessary noise from platform-list output