Support db file URL

[brody4hire]

As requested: https://groups.google.com/d/msg/cordova-sqliteplugin/PhJnDR7AxWU/JTlaZ7KZxRIJ

This could make it easier to store/access the db on Android sdcard (ref: #21), for example.

Target platforms should be Android and iOS, cannot break the WP(8) version. Supporting db file URL in the WP(8) version would be a plus.

This enhancement would make it easier to make this plugin work together with the File API plugin. I do not want to make this a dependency, however.

I cannot promise when I will have time to work on this. Pull request is welcome, however I do not want to include code from the Cordova File API or any other current plugins due to licensing issues (keep Android version with both MIT & Apache 2.0 license, iOS version has MIT license only since it was included from another project).

Where to look for hints:

• Android version: cordova-android framework/src/com/phonegap/FileUtils.java L245-L265 @ ff2ee67cb8 or cordova-android framework/src/com/phonegap/FileUtils.java L256-L276 @ 5a40613ccc
• iOS version: cordova-ios PhoneGapLib/Classes/File.m L219-L254 @ df67ab5f8b