Support custom source sets

[alexander-yevsyukov]

This PR:

1. Adds the ability to handle a custom source set in JS code generation.
2. Bumps dependency on tool-base and config.

Notable changes:

• GenerateJsonParsers action class introduced. The class encapsulates the code generation logic which was previously implemented as static methods under McJsPlugin.
• McJsExtension was renamed to McJsOptions.
• All path-related properties of the plugin options were removed (similarly to those in McJavaOptions).

[codecov]

Codecov Report

Merging #4 (64d687d) into master (ad26d3a) will increase coverage by 0.40%.
The diff coverage is 56.25%.

@@             Coverage Diff              @@
##             master       #4      +/-   ##
============================================
+ Coverage     93.38%   93.78%   +0.40%     
+ Complexity      253      249       -4     
============================================
  Files            43       44       +1     
  Lines           907      885      -22     
  Branches         32       33       +1     
============================================
- Hits            847      830      -17     
+ Misses           55       50       -5     
  Partials          5        5              

[alexander-yevsyukov]

@armiol, during my absence, if needed, please feel free to pick this PR up. Otherwise, I hope to pick it up on Monday next week.

[dmdashenkov]

LGTM with a small note.