Extracting base classes for analyzer factory and analyzers

[tulinkry]

Some base class is needed as a reference for the framework

This does not add any functionality. I verified both unit tests and index size does not change.

approaches #2588

[coveralls]

Pull Request Test Coverage Report for Build 3958

• 115 of 135 (85.19%) changed or added relevant lines in 53 files are covered.
• 4 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.005%) to 73.244%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
opengrok-indexer/src/main/java/org/opengrok/indexer/analysis/AnalyzerFactory.java	13	14	92.86%
opengrok-indexer/src/main/java/org/opengrok/indexer/search/context/Context.java	0	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/web/PageConfig.java	2	3	66.67%
opengrok-indexer/src/main/java/org/opengrok/indexer/search/SearchEngine.java	0	3	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/analysis/AnalyzerGuru.java	24	28	85.71%
opengrok-indexer/src/main/java/org/opengrok/indexer/search/Results.java	0	4	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/analysis/AbstractAnalyzer.java	24	30	80.0%

Files with Coverage Reduction	New Missed Lines	%
opengrok-indexer/src/main/java/org/opengrok/indexer/analysis/AnalyzerGuru.java	1	83.58%
opengrok-indexer/src/main/java/org/opengrok/indexer/search/Results.java	1	0.0%
opengrok-indexer/src/main/java/org/opengrok/indexer/history/BazaarRepository.java	2	70.16%

Totals
Change from base Build 3954:	0.005%
Covered Lines:	32790
Relevant Lines:	44768

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💛 - Coveralls

[tarzanek]

lgtm, merging