Added easy Maven integration with two batch files

Easy Maven integration using the Android Maven apklib structure.
The generate_apklib batch file will use 7-zip to generate an apklib zip
file containing the files enumerated in apklib.txt.

mvn_install.bat will install aFileChooser to the local Maven repository
with the following information:

groupId: com.ipaulpro
artifactId: afilechooser
version: 1
type: apklib

Since it uses batch files, this is a Windows-only addition, but fortunately the command structure in the two batch files should copy-paste directly into a bash script without any modification.

[See the wiki article for the Android Maven plugin on this subject.](https://code.google.com/p/maven-android-plugin/wiki/ApkLib)