Implement GEM-mappability reader

[magicDGS]

Includes

• Header abstraction
• Mappability record
• Exceptions
• Reader

Part of #207

[codecov[bot]]

Codecov Report

Merging #480 into master will decrease coverage by 0.292%. The diff coverage is 87.407%.

@@              Coverage Diff               @@
##              master     #480       +/-   ##
==============================================
- Coverage     93.412%   93.12%   -0.292%     
- Complexity       991     1042       +51     
==============================================
  Files             95       99        +4     
  Lines           2641     2776      +135     
  Branches         284      299       +15     
==============================================
+ Hits            2467     2585      +118     
- Misses           133      145       +12     
- Partials          41       46        +5

Impacted Files	Coverage Δ	Complexity Δ
...utils/mappability/gem/GemMappabilityException.java	100% <100%> (ø)	5 <5> (?)
...ls/utils/mappability/gem/GemMappabilityHeader.java	58.333% <58.333%> (ø)	12 <12> (?)
...ls/utils/mappability/gem/GemMappabilityRecord.java	90% <90%> (ø)	6 <6> (?)
...ls/utils/mappability/gem/GemMappabilityReader.java	98.765% <98.765%> (ø)	28 <28> (?)