GPII-182: Removing call to g_type_init

g_type_init function has been deprecated since glib version 2.36,
see: https://developer.gnome.org/gobject/stable/gobject-Type-Information.html#g-type-init
GPII-182: Declare variant and type just once

This change fixes the "variable ‘type’ set but not used" warning
GPII-182: Add a return value to get_gsetting function

This change fixes the "control reaches end of non-void function" warning
GPII-259 Initial source code of the Xrandr Node.js

[Includig]
  - Adding the add-on structure.
  - A brief demonstration of how this add-on should be used is included
    into
    nodexrandr_tests.js file.
  - Adding a getDisplays method. It returns some information about the
    displays.
  - Adding a getBrightness method. It returns the current brigthness
    value.
  - Adding a setBrightness method. It sets the brigthness level.
  - Adding a dummy setScreenResolution method. Still requires some work.
GPII-259: Implementing setScreenResolution method
GPII-259: Adding jqUnit tests for the Xrandr bridge
GPII-259: Creating an Xrandr Settings Handler

[changes]
- Adding:
  - gpii.xrandr.getBrightness
  - gpii.xrandr.getScreenResolution
  - gpii.xrandr.setBrightness
  - gpii.xrandr.setScreenResolution
GPII-259: Adding the xrandr module to be loaded at start
GPII-259: Adding a few jqUnit tests for the Xrandr Settings Handler
GPII-259: Include the Xrandr add-on into the build system
GPII-259: Code cleanup
GPII-343: Adding a Node.js bridge to call ALSA

[changes]
  * Adding both methods to get and set the master volume
  * Adding binding.gyp
  * Adding some tests at add-on level
GPII-343: Adding a Settings Handler for ALSA

[changes]
  * Adding package.json
  * Adding a Settings Handler which uses the Node.js ALSA volume bridge
  * Adding tests for the ALSA Settings Handler
GPII-343: Adding the new ALSA stuff into the GPII

[changes]
  * Add alsa into both build and clean processes
  * Add alsa into Linux's index.js in order to be loaded by the
framework at start time
GPII-343: In build.sh, update the comment for ALSA
GPII-343: Setting max and min values for volume range

This change will avoid errors while transforming values, no need to
round numbers, etc.
Merge remote-tracking branch 'javihernandez/GPII-182'
Merge remote-tracking branch 'javihernandez/GPII-343'
Merge remote-tracking branch 'javihernandez/GPII-259'

Conflicts:
	build.sh
	clean.sh
	gpii.js