Prevent File System Cache Conflicts

[schrieveslaach]

This change attempts to fix the constant display of “File Cache Conflict” dialogs.

Fixes #16

[schrieveslaach]

@blinry, @zormit, FYI I came across a bug in teamtype while trying to fix #16, see teamtype/teamtype#497

[schrieveslaach]

Things I've tried so far:

• implement a com.intellij.openapi.fileEditor.FileDocumentSynchronizationVetoer: mayReloadFileContent after the dialog popped up, so the user still gets annoyed by the dialog
• implement com.intellij.openapi.vfs.WritingAccessProvider: turns the editor into read-only mode so the user cannot make changes.
• implement com.intellij.openapi.vfs.VirtualFileSystem as a facade for "file" protocol so that I can redirect write to /dev/null: Intellij does not allow to do that. Only new protocols can be added.

This PR so far provides a couple of more unrelated improvements. I'll pull them out bring them to the mainline branch.