NEMO#260 Gallery can now show and play videos with basic control

First of all, a video player with basic controls has been added (VideoPlayer.qml).
The video player doesn't have any control due to a flickering issue which appear when any UI component
in the same view as the video player is drawn. GalleryModel now uses File as rootType and it has a filter
on video/* and image/* mimeTypes to be able to show both videos and images. Moreover, a QGLWidget has
been set as QDeclarativeView's viewport to avoid lag issues which would occur for the whole lifecycle of
the application after playing the first video.
Two different mouse areas are now used to detect clicks on the images when the image is zoomed in and
when it is not. That is to avoid conflict between the many mouse areas used in this application.
Many more small adaptation changes have also been applied. Hacky solutions have been documented in the
code using comments.
remove property int because index is already defined in the component
Fixes a bug with the images not being correctly aligned in one case

This fix makes image align properly.
Previously, images were not aligned correctly when the videoplayer was
started in portrait mode, and was popped after rotating the phone in
landscape mode. This was due to flickTo NumberAnimation breaking the binding
on leftMost.x.

A new Binding element has been added to control this behaviour, and
a new bool property (keepMiddleItemCentered) has been added to control that
binding. The developer has to set keepMiddleItemCentered to false when he
wants to modify the x value of the leftMost item manually, and he has to set
it back to true once he has finished such modifications, to be sure that the
leftMost item is correctly positioned, thus showing the "middle" item in the
center of the screen.
NEMO#407 Deleted deprecated ENCODING key from .desktop file

Note to the person who will tag the new version and release it:
Add the following line to the .changes file:
- NEMO#407 Deleted deprecated ENCODING key in the .desktop file
Merge pull request #1 from faenil/desktopfix

NEMO#407 Deleted deprecated ENCODING key from .desktop file
last fixes
Merge branch 'add_video_part1' of https://github.com/faenil/qmlgallery into add_video_part1
Merge pull request #9 from faenil/add_video_part1

NEMO#260 Gallery can now show and play videos with basic control
NEW FEATURE: show videos only or images only option added in gridview menu

Code to create and modify filters dynamically has been added.

This will make it easier to implement new filtering features
Merge pull request #10 from faenil/sorting

NEW FEATURE: show videos only or images only option added in gridview me...
Removed log message when using an invalid index

It's not needed, I'd rather check the index value all times before calling isVideo(index)
NEMO#400 Removed debug message when rotating the device in gridview
Added possibility to sort by date taken, file name and file extension
Changed sort and filter to be shown using same loader. Added possibility to sort files by type and name, and in addition pictures by date taken.
Removed debug message and void comment.
Removed commented code, fixed copy paste bug
Removed date taken sorting and hacks accompanied with it
minor cleaning
Merge pull request #11 from arisilen/filtering

NEMO#258 Added possibility to sort by date taken, file name and file extension
Fix warning about non-existent imgController property