Make rope/jedi module pre-loading configurable

[gatesn]

Right now there's a statically defined list of modules that we try to eagerly import. At the cost of memory, this can drastically reduce the time-to-first-completion.

[randy3k]

Is it the reason why the directory .ropeproject is still created even when rope_completion is not enabled?

[evandrocoan]

@randy3k, the .ropeproject folder currently cannot be disable by user settings because the python-language-server receives the settings from the language client, after loading the server plugins: #253 (comment)

python-language-server/pyls/workspace.py

Lines 84 to 89 in b0dc780

	# Whilst incubating, keep private
	if self._lang_server.config.plugin_settings('rope').get('create_folder', False):
	self.__rope = Project(self._root_path)
	else:
	self.__rope = Project(self._root_path, ropefolder=None)
	self.__rope.prefs.set('extension_modules', self.PRELOADED_MODULES)

This way we cannot configure the plugins load options. But you can change directly your client code as the one above to pass by default ropefolder=None. This way the ropeproject folder is never created.

[gatesn]

@evandrocoan we cannot delay loading the plugins for the didChangeConfiguration message because it may never come.

Instead I've proposed this: https://github.com/palantir/python-language-server/pull/298/files

Which lazily construct a rope project, and creates a new one if the rope config changes.