Test against multiple AS and Sinatra versions

This enables testing against Sinatra Edge and multiple activesupport versions. The change also
lowers the activesupport dependency to 3.1.

Failures in Sinatra Edge tests are ignored
Less matrix entries for sinatra_edge and ActiveSupport

Travis is free, so don't tax it too much with matrix entries that don't give much gain.
Merge remote-tracking branch 'origin/master' into multi-as-testing

Conflicts:
	.travis.yml
Track modules independent of gems and care less about gems
Merge pull request #1003 from padrino/multi-as-testing

Test against multiple AS and Sinatra versions
Updated static assets
Added a missing dependency for padrino-helpers in padrino-cache. See #719.
Merge pull request #1021 from padrino/add-helpers-as-dependency-for-cache

Added a missing dependency for padrino-helpers in padrino-cache
Merge remote-tracking branch 'origin/master' into apps-in-gems