Explicitly cast input to integer

While working with angularifying the add prefix page I noticed that
integer parameters needed to be cast to integer explicitly in the XHR
controller. This commit addresses that.
Added Pylons ng-ctrllr for single-page-ish pages

Added a new 'ng'-controller to Pylons for single-page-ish AngularJS
pages. In the future this can probably be replaced with a static HTML
page, but currently I judged this the best balance between avoiding
touching too much code (for example the hilighting of the current
section in the top menu bar, which still is handled by the Jinja2
templates) and enabling AngularJS functionality.

Added a prefix-action to the ng-controller which handles prefix-related
pages.
Moved angularified add-prefix page to ng-ctrllr

Moved the AngularJS-version of the add-prefix page from an own action in
the Pylons prefix controller to the new Pylons 'ng'-controller. The
prefix allocation method (from-prefix, from-pool or manual) can be
passed to the controller as URL parameters, optionally together with a
parameter to the allocation method (ID of a prefix to allocate from in
case of from-prefix, ID of pool to allocate from in case of from-pool).

Also did some fixes for allocation from prefix to work properly.
Added links to angularified add prefix page

Added links to the angularified add prefix-page, including allocation
method and parameter, from the pool list and prefix list.