[Tools] Add tools/increment-version.py.

This is a fork of the tool with the same name present in the crosswalk
repository. It increments the version number for canaries (and other release
types in the future), and is called primarily by the canary building
infrastructure.
Merge pull request #196 from rakuco/add-increment-version

[Tools] Add tools/increment-version.py.
[Power] Share state changed callback between instances

The power.h library in Tizen only allows one callback for tracking state
changes, so we make this tracking for the extension, since we can have
multiple instances. Instances now add (and remove) themselves to
PowerEventSource.
[Power] Fix JS style.

Yet another style fix.
Merge pull request #198 from darktears/power-style-fixes

[Power] Fix JS style.
Merge pull request #197 from cmarcelo/power-event-source

[Power] Share state changed callback between instances
[Power] Keep only one listener

Keeping a list is confusing since we don't really support multiple
listeners. Also done some JS cleanup. This shouldn't change the
behavior.
[Power] Lazily fill defaultScreenBrightness

This avoids all the tests sending a sync message to PowerInstance
without need. It is also a good practice to not do blocking work during
initialization if that could be avoided.
[Power] Send change events only if there's someone listening

Add a new message SetListenToScreenStateChange, from JS to native, that
will be used to tell native that we have a listener. This patch also
ensures that we have a proper value to be used as "old state", by
getting the value at time of listener registration.

One consequence is that after this patch, tizen.power code is not called
at all unless the page uses tizen.power features.

This patch should reduce a lot the errors related to invalid sync
messages, they were caused mostly by those setup messages when running
tests that loaded pages repeatedly.
Merge pull request #199 from cmarcelo/power-fixes

[Power] Reduce message exchange at initialization, as well as unneeded messages
Add a VERSION file.

It works the same way the one in crosswalk does: it represent's the current
version number, with MAJOR and MINOR numbers in different lines.

There is no use for it in-tree at the moment, but it is useful for the build
infrastructure to have it around.
Merge pull request #200 from rakuco/add-VERSION

Add a VERSION file.