Remove image caching from Deployable model

The caching was added because the image details were queried from ImageWarehouse over HTTP. With TIM, it's all stored in DB, so no need for this kind of caching.
Ruby 2.0 compatibility: remove implicit conversion of nil into String
Update Gemfile to use HTTPS requests

The source :rubygems is deprecated because HTTP requests are insecure.
Add Ruby 2.0 to Travis
Remove unused ProviderSelection code
remove unused untested controller api/environments
remove hooks: unfinished and probably obsolete hook controller, model, tests, views
Merge pull request #420 from martinpovolny/remove_api_environments

remove unused untested controller api/environments
Merge pull request #419 from ifarkas/remove_unused_provider_selection_code

Remove unused ProviderSelection code
code style cleanup in models
Merge pull request #418 from ifarkas/ruby2.0-compatibality

Fix Ruby 2.0 compatibility issues
Merge pull request #422 from martinpovolny/coding_style

code style cleanup in models
Remove unused utils/conductor code
Merge pull request #423 from ifarkas/remove_unsued_methods_from_utils_conductor

Remove unused utils/conductor code
Enable slow query warnings in development environment

This feature was introduced in Rails 3.2 and is enabled by default in new projects.
Merge pull request #428 from ifarkas/auto_explain

Enable slow query warnings in development environment
Merge pull request #417 from ifarkas/catalog_image_cache

Remove image caching from Deployable model
Merge pull request #421 from martinpovolny/remove_api_hooks

remove hooks