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