IDE-1567 Add LiferayMessageErrorTagCompletionProposalComputer for lifera...

IDE-1567 Add LiferayMessageErrorTagCompletionProposalComputer for liferay-message/liferay-error tag
Lets break up the method some to not make it so long.  Do all of the if() checking in some method like hasLiferayMessageErrorTag() type checking, before we do the calculation.