feat(snowowl.core): Small change required for downstream project

[apeteri]

• Make test dependencies of com.b2international.snowowl.validation.snomed optional so that they do not need to be included in launch configurations
• Make the RF2 importer for relationships less strict, allowing matching sourceId and destinationId values for non-IS A relationships
• Add Java system property that allows extending the list of Java packages to inspect during classpath scanning (the property name is so.component.scan and it expects a comma-separated list of package names as its value)

[nagyo]

LGTM!

[codecov]

Codecov Report

Attention: Patch coverage is 63.63636% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 48.34%. Comparing base (5d787b2) to head (039b1c7).
Report is 2 commits behind head on 9.x.

Files	Patch %	Lines
.../src/com/b2international/snowowl/core/SnowOwl.java	55.55%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                9.x    #1294      +/-   ##
============================================
- Coverage     48.35%   48.34%   -0.01%     
- Complexity    13976    13978       +2     
============================================
  Files          1947     1947              
  Lines         95154    95163       +9     
  Branches      10997    10999       +2     
============================================
+ Hits          46007    46010       +3     
- Misses        46134    46139       +5     
- Partials       3013     3014       +1     

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