Remove usages of the `jcenter()` Maven repository from build scripts

This merge request depends on 2 other merge requests being merged

Closes #209 (closed); Remove usages of jcenter() Maven repository from build scripts.

NOTES:

• Replaced jcenter() usages from build.gradle (Project: NEST) with mavenCentral()
• Removed the following implementations:
  • me.dm7.barcodescanner:zxing:1.9.13
  • com.karumi:dexter:5.0.0
• Copied code from AbstractScannerFragment.java to a newly created AbstractScannerActivity.java class
  • Updated the copied code to work as an activity
• Converted the deprecated class: edu.ncc.nest.nestapp.Scanner.java to use the new scanner implementation by extending the new AbstractScannerActivity.java class
• Converted the class edu.ncc.nest.nestapp.UPCScanner.java to use the new scanner implementation by extending the new AbstractScannerActivity.java class
• Also updated the following to the latest versions: gradle, google-services, firebase implementation, and app-compat implementation

ADDITIONAL NOTES:

• Renamed package edu.ncc.nest.nestapp.AbstractScannerFragment to edu.ncc.nest.nestapp.AbstractScanner
• Renamed layout file fragment_abstract_scanner to abstract_scanner since it is used in both AbstractScannerFragment.java and AbstactScannerActivity.java`
• Decided to convert the classes to the new scanner implementation instead of deleting them, to leave the old functionality in the app for now.
  • In the future, AbstractScannerActivity.java may be able to be removed if it is no longer needed