Completion attempts get confused by existing yang prefix, and don't use it to qualify candidates

[davidmichaelkarr]

Completion attempts use the existing symbol prefix to determine candidates.

This needs to treat "prefixes" like "modname:symb" differently. Instead of looking for a symbol that begins with "modname:symb", it needs to look for symbols that begin with "symb" in the module with declared prefix "modname".

[davidmichaelkarr]

This can be resolved by changing "YangSimpleCompletionProcessor.getProposalsByMode()" by looking for the colon in the prefix, and determining the module name by passing the prefix before the colon to "module.getImportByPrefix()" and passing that returned module name to "getUsesProposals()" and "getTypeProposals()" (along with adding the second formal parameter to accept this), and then passing that module name to the call to "YangModelManager.search()" in each of those methods. This could also be applicable to other "get*Proposals()" methods, but I have to think about what those mean yet.