[maven-release-plugin] prepare for next development iteration
changed to use plugin testing from ASF now that 3.0.0 is finally released
Better consumption of AAR during APK build.

GenerateSourcesMojo#generateR more closely follows AndroidBuilder way of building.

GenerateSourcesMojo#addResourceDirectories was modified to only add a single combined res folder as per AndroidBuilder. I'm unsure whether in doing so I have cut out something critical and whether this is correct/safe/good. But it's what AndroidBuilder does and it works.

ApklibMojo was changed so that it includes R.txt into APKLIB builds. This means we have a ready way of generating R for the APKLIB when creating the APK without having to invoke appt more than once.

 If we need to support APKLIB with no R.TXT then we can uncomment the #generateRForApklibDepedency method in ResourceClassGenerator and force it to work.

NB Have been testing this against the android-maven sample-libraryproject modified to include aar1-lib1 and librarypojects-lib2 as the 2 dependent libs of mainapp. I will generate a pull request for that too once I have added in a few more items that will better test all scenarios.
Removed --debug-mode from aapt.
Fixed a bug that was causing the packaging to crash because it was looking for resources on both combinedRes folder as well as all other resource folders, so it was finding it twice.
Add compatibility for apklib & aar to be mixed together in an apk
upgraded powermock to 1.5.2
Not packaging R.txt into apklib.
R generated for apklib now only contains resources for that apklib.
Verify the existence of the apklib asset folder
updated to android builder 0.7.0 and sdkjars 22.4.0
ConsumeAarMojo needs to occur @ compile when project is apklib and aar too.
Adding resources and assets of apklib dependencies into aapt when generating R for apklib
updated to android builder 0.7.1
Using the apklib dependency's folder and not the project's folder when appending the manifest and apklib's dependencies.
Only supplying a single assets folder argument to aapt.
This is achieved by merging all assets into a single combined-assets folder for each artifact that we need to invoke aapt for.
Defined PullParameter#defaultValue as []

This allows to declare empty strings as default values: {""}; additional
checks occurs @runtime
inject MojoExecution
Use ExpressionEvaluator in ConfigHandler to get default values
get the default value of proguard outputDirectory from @PullParameter