Using Doctrine\Common\Persistence classes.

Using Doctrine\Common\Persistence classes (ObjectManager and ObjectRepository)
in place of Doctrine\ORM classes (EntityManager and EntityRepository).
Fixed page titles site-wide.

Updated the page titles site-wide to reflect the actual content
of the page. Also added the description meta field which is empty for now,
but needs to be filled in with the appropriate copy.
Added the ability to remove availabilites from schedule.

Rundown of changes:

- `getAvailability()` is now `isAvailabile()`, the latter reads better.
- Cleaned up error messages.
- Added error messages to the schedule view.
- Touched up styles for new form elements.
- Refactored Schedule* entity tests to use new methods name.

Closes #35.
Fixed box-sizing issue.
Added browser support to the README file.

Closes #27.
Added a bit more context to the contributing file.
Removed unneeded namespace imports.