VIM-652 Add support for executing and mapping arbitrary IDEA actions

* no tests performed..! *

Example usage:
:nnoremap gi :action GotoImplementation<CR>
:nnoremap gu :action FindUsages<CR>
:nnoremap gcw :action RenameElement<CR>

Action overview:
https://github.com/JetBrains/intellij-community/blob/6c6cb47c5a41025549157d64643a98a89481260d/platform/platform-resources-en/src/messages/ActionsBundle.properties