add new sorting methods for file list in filemanager
Now files can be sorted by filename or last accessed time
Merge pull request #1073 from chrox/fulltext_search

add new sorting methods for file list in filemanager
Refactoring hardware abstraction

This is a major overhaul of the hardware abstraction layer.
A few notes:

General platform distinction happens in
  frontend/device.lua
which will delegate everything else to
  frontend/device/<platform_name>/device.lua
which should extend
  frontend/device/generic/device.lua

Screen handling is implemented in
  frontend/device/screen.lua
which includes the *functionality* to support device specifics.
Actually setting up the device specific functionality, however,
is done in the device specific setup code in the relevant
device.lua file.

The same goes for input handling.