IDE-1567 Add LiferayMessageErrorTagCompletionProposalComputer for lifera...

IDE-1567 Add LiferayMessageErrorTagCompletionProposalComputer for liferay-message/liferay-error tag
languagePropertiesLastModified is for all files across all projects?  That is not right because you could modified files that are younger than previous version but older than this global languagePropertiesLastModified, this needs to be redesigned.