Implement LDAP user lookup.

This is required to improve compatibility when the DN cannot be easily
computed from the user name. Additionally, this allows automatically
getting the full name and email address from LDAP.
Use popover to edit task and description directly from board.

- Click on 'description' icon opens the 'edit-description' page.
- Edit task and edit description now open in popover, like the assign
dialog.
Allow 'no category' and 'unassigned' in actions.

This can be used to assign a color to task with no category/assignee, or to reset
assignee.
Add closeTask jsonrpc API.
Add openTask jsonrpc API.
Add option to disable SSL certificate verification for LDAP.
Merge pull request #165 from Typz/closetask

Add openTask and closeTask jsonrpc API.
Merge pull request #163 from Typz/popover

Use popover to edit task and description directly from board.
Merge pull request #164 from Typz/actions

Allow 'no category' and 'unassigned' in actions.
Merge pull request #161 from Typz/ldap

Implement LDAP user lookup.
Add Postgresql support
Add a new contributor
Integration of the chosen jquery plugin for the board selector
Fix bug: due date and score lost on update
Improve javascript code and remove CSP errors
Add fields: task creator and modification date
Minor changes for the LDAP model
Show task count in each column even if no limit is set (merge pull-request #169)
Merge pull-request #171: many fixes (Vagrant file, German locales and CSS)
Merge pull-request #147 and #146 (autofocus for comment and description textarea)