Add checker for String boundary

...nz/fgbks/base/utils/boundary/AbstractGrowingBoundary.java

...fgbks/base/utils/boundary/checker/CheckIsSubsumption.java

...blenz/fgbks/base/utils/boundary/checker/CheckOverlap.java

...z/fgbks/base/utils/boundary/checker/CheckStringEqual.java

...bks/base/utils/boundary/checker/CheckStringInContact.java

.../base/utils/boundary/checker/CheckStringNotInContact.java

...fgbks/base/utils/boundary/checker/CheckStringOverlap.java

...gbks/base/utils/boundary/checker/CheckStringSubsumes.java

...s/base/utils/boundary/checker/CheckStringSubsumption.java

...oblenz/fgbks/base/utils/boundary/impl/StringBoundary.java

...e/utils/boundary/checker/CheckStringNotInContactTest.java

.../base/utils/boundary/checker/CheckStringSubsumesTest.java