Support standard doclet visibility options in UML

[sjoerdtalsma]

This partially fixes #148

Still to be implemented are support for:

• --show-module-contents (see Test (& add) --show-module-contents support #150)
• --show-packages (see Test (& add) --show-packages support #151)

Maybe the env.isIncluded() method already solves these for us, but that still needs to be tested.
I will submit new issues for these.

[coveralls]

Pull Request Test Coverage Report for Build 909

• 34 of 34 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 94.286%

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Totals
Change from base Build 898:	0.5%
Covered Lines:	1518
Relevant Lines:	1610

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💛 - Coveralls