Improve some minor design stufs

Changes some colors and borders for the days and exercises lists,
fix the image responsiveness on the index page and add a new
background image too.

Conflicts:
	traintool/src/frontend/Gruntfile.js
	traintool/src/frontend/app/adapters/transformers.js
	traintool/src/frontend/dependencies/assets/sass/screen.scss
Add transition when workout is created

This commits fix utc problem when retrieving dates from the
rest api and adds a transition to the workout visualization when
it's created.
Change same design stuffs

Change colors of the elements used to list days and exercises.
Add proper time validator

This commit adds validation to the proper time field on a day
creation.
Merge branch 'master' of github.com:AEHO/traintool
Merge branch 'bug/minor_fixes'
Remove a useless image