Add support for `focus` tags in specs

Adding `focus: true` to specs, will filter out all other specs, running
only the ones with the `focus` tag.
Remove "My characters" navigation item

Since the main menu item goes to the same place, we sholdn't have
dplicate menu items.
Improve look and feel of "level up bar"
Adding multitenancy

This patch adds the Mongoid::Multitenancy module, which scopes all
characters under the current user.

However, this is only applicable, when a current user is set. Otherwise,
the character will be unscoped. This should be metigated by forcing a
user login (at the moment this is expected to happen with devise).
Associate characters to users.

This scopes all calls in the characters controller within the current
user. This means, that users can only manage their own character.

Creating a new character will assign it to the current user.
Allow users to level up a character

This allows the user to add a level to his character, if the character
is elligable for leveling up (e.i. `level_up?` is true).
Improve tabs when editing a character

When editing a character, this patch improves the tabs by allowing deep
linking. It also fixes a bug, where all content divs would show up, when
no deep linking hash was given.

It also adds jquery cookie, which should be used to store tab selection
in the user's browser, at some point.