Mechanism to exclude files from check

[petertrr]

What's done:

• Logic in maven plugin
• Logic in gradle plugin
• Tests in gradle plugin
• Fixes for metrics_yml

This pull request closes #325 , also partially closes #543

Added excludes in maven plugin in diktat self-check.
I've tested excludes in gradle plugin manually.

Fixme

• Update readmes
• check if package in metrcs_maser actually helps, or will it not find diktat-common

[codecov]

Codecov Report

Merging #563 (ff1651f) into master (052bd9d) will decrease coverage by 0.94%.
The diff coverage is 84.84%.

@@             Coverage Diff              @@
##             master     #563      +/-   ##
============================================
- Coverage     81.68%   80.73%   -0.95%     
- Complexity     1641     1702      +61     
============================================
  Files            79       87       +8     
  Lines          4139     4345     +206     
  Branches       1307     1340      +33     
============================================
+ Hits           3381     3508     +127     
- Misses          229      299      +70     
- Partials        529      538       +9     

Flag	Coverage Δ	Complexity Δ
unittests	80.73% <84.84%> (-0.95%)	0.00 <39.00> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
...lin/org/cqfn/diktat/plugin/maven/DiktatBaseMojo.kt	7.14% <0.00%> (ø)	2.00 <0.00> (?)
...at-rules/src/main/kotlin/generated/WarningNames.kt	0.00% <ø> (ø)	0.00 <0.00> (ø)
...fn/diktat/ruleset/rules/kdoc/CommentsFormatting.kt	69.79% <ø> (-0.21%)	76.00 <0.00> (-1.00)
...lin/org/cqfn/diktat/ruleset/rules/PackageNaming.kt	93.75% <33.33%> (-1.19%)	32.00 <0.00> (ø)
...qfn/diktat/plugin/gradle/DiktatJavaExecTaskBase.kt	76.92% <72.72%> (ø)	6.00 <0.00> (?)
.../cqfn/diktat/ruleset/rules/BlockStructureBraces.kt	83.92% <85.71%> (+0.11%)	53.00 <0.00> (ø)
...ktat/ruleset/rules/AvoidEmptyPrimaryConstructor.kt	90.00% <90.00%> (ø)	8.00 <8.00> (?)
...iktat/ruleset/rules/ImplicitBackingPropertyRule.kt	93.75% <93.75%> (ø)	23.00 <23.00> (?)
...n/org/cqfn/diktat/plugin/gradle/DiktatExtension.kt	100.00% <100.00%> (ø)	5.00 <1.00> (?)
...rg/cqfn/diktat/plugin/gradle/DiktatGradlePlugin.kt	100.00% <100.00%> (ø)	2.00 <0.00> (?)
... and 19 more

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[orchestr7]

lgtm