Rewrote LibGroup to use api instead of parsing document

[nedius]

Closes #2998 and #2660

Checklist:

• [X] Updated extVersionCode value in build.gradle for individual extensions
• [X] Updated overrideVersionCode or baseVersionCode as needed for all multisrc extensions
• [X] Referenced all related issues in the PR body (e.g. "Closes #xyz")
• [X] Added the isNsfw = true flag in build.gradle when appropriate
• [X] Have not changed source names
• [X] Have explicitly kept the id if a source's name or language were changed
• [X] Have tested the modifications by compiling and running the extension through Android Studio
• [x] Have removed web_hi_res_512.png when adding a new extension