Add BoundaryLayer - a helper for drawing foci boundaries

[ekigamba]

Fixes #256

[coveralls]

Pull Request Test Coverage Report for Build 1223

• 61 of 155 (39.35%) changed or added relevant lines in 3 files are covered.
• 10 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.7%) to 32.364%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sample/src/main/java/io/ona/kujaku/sample/activities/BaseNavigationDrawerActivity.java	0	3	0.0%
sample/src/main/java/io/ona/kujaku/sample/activities/FociBoundaryActivity.java	0	44	0.0%
library/src/main/java/io/ona/kujaku/layers/BoundaryLayer.java	61	108	56.48%
<!--	Total:	61	155	39.35%	-->

Files with Coverage Reduction	New Missed Lines	%
library/src/main/java/io/ona/kujaku/utils/LogUtil.java	10	0.0%
<!--	Total:	10		-->

Totals
Change from base Build 1216:	0.7%
Covered Lines:	1580
Relevant Lines:	4882

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💛 - Coveralls