Add a file explorer (#1861)

* Adds a File Manager pane. Jumps to folder or file when open project.

* Better activation of file or directory opened

* First working version of File panel.
Double click of files to open, in RIDE or external simple editor.

* Minor refactoring

* Feature: When invalid data file, open in Code Editor

Author: HelioGuilherme66

src/robotide/controller/project.py

@@ -152,6 +152,8 @@ def load_datafile(self, path, load_observer):
         if datafile:
             return datafile
         load_observer.error("Invalid data file '%s'." % path)
+        e = UserWarning("Invalid data file")
+        return e
 
     def _load_datafile(self, path, load_observer):
         datafile = self._loader.load_datafile(path, load_observer)