BB10: Some changes to layout

- Tabbed interface was replaced with single page. Signature action is
  used for performing search.
- Action bar now hiddes itself when scrolling About page content.
- style.js file with constants to be used all over the application
  (values are in device units).
- About page now uses new style.js file.
- SystemToast is shown in the top center of the application window.
- `osVersion` not needed.

See #100 - Cascades UI for BlackBerry 10
Incapsulate `StationsListModel::m_list`...

...and provide public accessors to manipulate it.
BB10: Provide BB10 specific data model in StationsListModel

Implemented as QMapListDataModel for now. Should be replaced with custom
model which is more tailored for our needs in future.

See #100 - Cascades UI for BlackBerry 10
BB10: Station search and selection

See #100 - Cascades UI for BlackBerry 10
WIP: Cascades UI