refactored getPackageName()
moved classes about apk. It was mistake to have placed those classes
under database.
merged the ApkInfo into the Apk. These entities were actually the same.
Then added to the table those columns that belonged to ApkInfo.
fixed lowercase to uppercase in the sql statement.
changed the way how to get the apk information from "aapt" to "apktool".
Since "apktool" can decode the AndroidManifest.xml, it is possible to
parse the apk information as XML.