Funcotator - Adding cDNA Strings for Intronic Variants

[jonn-smith]

Added in cDNA strings for intronic variants.

Now intronic variants produce a cDNA string.  This string is created in
a similar way to how the Codon Change String is created for intronic
variants:

If the transcript containing the variant has no exons, the cDNA string
will be empty.

If the transcript in which the variant occurs contains at least 1 exon, the string will be non-empty and of
the form:
    c.e[EXON NUMBER][+|-][BASES FROM EXON][REF ALLELE]>[ALT ALLELE]
Concretely:
    c.e2-1A>G
Where:
     2 = the number of the exon to which the given variant start is closest
    -1 = number of bases away from the exon (1 before)
     A = Reference allele
     G = Alternate allele

Fixes #5187

[LeeTL1220]

@jonn-smith Minor stuff. Feel free to merge once it is addressed.

[LeeTL1220]

@jonn-smith Make sure to check that travis errors are transient.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@8c696a4). Click here to learn what that means.
The diff coverage is 98.765%.

@@            Coverage Diff             @@
##             master     #5321   +/-   ##
==========================================
  Coverage          ?   86.906%           
  Complexity        ?     30311           
==========================================
  Files             ?      1849           
  Lines             ?    140500           
  Branches          ?     15475           
==========================================
  Hits              ?    122103           
  Misses            ?     12788           
  Partials          ?      5609

Impacted Files	Coverage Δ	Complexity Δ
...er/tools/funcotator/FuncotatorIntegrationTest.java	85.968% <0%> (ø)	111 <0> (?)
...Sources/gencode/DataProviderForPik3caTestData.java	98.684% <100%> (ø)	3 <0> (?)
...dataSources/gencode/GencodeFuncotationFactory.java	86.294% <100%> (ø)	187 <0> (?)
...Sources/gencode/DataProviderForMuc16IndelData.java	94.444% <100%> (ø)	1 <0> (?)
...e/hellbender/tools/funcotator/FuncotatorUtils.java	87.812% <100%> (ø)	191 <8> (?)
...nder/tools/funcotator/FuncotatorUtilsUnitTest.java	92.62% <100%> (ø)	85 <7> (?)
...urces/gencode/DataProviderForMuc16MnpFullData.java	99.952% <100%> (ø)	6 <0> (?)