Add check for duplicate keyword names

[daluu]

Per the Java remote server and JavaLibCore:

Both JavalibCore(AnnotationLibrary) and jrobotremoteserver check for duplicate keywords (my_keyword and myKeyword for example). When a duplicate is found the library is not loaded or imported. I'm not sure what RF does if the dynamic library returns conflicting keywords.

Code: https://github.com/robotframework/JavalibCore/blob/master/src/main/java/org/robotframework/javalib/factory/AnnotationKeywordFactory.java#L77 Test: https://github.com/robotframework/JavalibCore/blob/master/src/test/robotframework/acceptance/annotationlibrarywithmultiplepatternsandconflictingkeywordnames.tsv Code: https://github.com/ombre42/jrobotremoteserver/blob/master/src/main/java/org/robotframework/remoteserver/javalib/SimpleKeywordFactory.java#L66 Test: https://github.com/ombre42/jrobotremoteserver/blob/master/src/test/java/org/robotframework/remoteserver/javalib/SimpleKeywordFactoryTest.java