Add a codestyle for Android Studio / intellij.

Copied from Android Open Source Project at
https://github.com/android/platform_development/commit/87cfafaa3d9ebebe6a60d7919fe6b4dfb62a7bf0

Update HACKING.md to describe how to install and enable this style in
Android Studio.
Remove unused imports.
Convert mScanBtn to a local variable instead of a field.
Remove unnecessary semi-colons.
Remove redundant local variables.
Remove empty onCreateOptionsMenu() method.
Suppress EmptyMethod warnings for onPreExecute() and onCancelled().
Remove redundant initialiser.
Remove redundant "artwork" variable.
Add pragma to disable warning for valid empty if() body.
Remove empty switch statement.
Remove unused variable "parameters".
Use 0dip instead of wrap_content for more efficient layout_height.
Use "sp" instead of "dp" for textSize to honour user's preferences.
Enable Proguard for gradle builds.

Split the Proguard configuration in to several files, one for
Android defaults ("proguard.cfg"), one per library that has special
Proguard requirements ("proguard-acra.cfg", "proguard-guava.cfg")
and one for things that are specific to Squeezer.

Guava needs the "jsr305" library installed to work with Proguard,
so add that as a dependency.

Customise the "release" buildType to run Proguard and use these
configuration files.

Add a signingConfig to the "live" product flavour so that it shows up
in the list of tasks.  Use the debug signing config for the moment.
Update gradle config to support signing releases.

Create gradle.properties, which defines a property file called
'squeezer.properties'.  This file (not checked in to source control)
contains two entries:

  key.store.password=...
  key.alias.password=...

defining the values for those passwords.

Update build.gradle to look for this file (indirectly, through the
value of "Squeezer.properties") and use the values from it if it exists.
If it doesn't exist then provide dummy values to allow the other tasks
to complete.
Merge remote-tracking branch 'nik/actionbar' into actionbar