Enable the indent options in code style settings (fixes #908)

[virtulis]

This is a near-exact copy of the solution proposed by @trnzk in the #908 comments, except for the added this parameter.

Unfortunately I have no experience in IDEA plugin development so can't write a proper test for this at the moment.

However I have tested it manually and verified that it works:

• "Tabs and Indents" tab in the settings is now present.
• Selecting "Use tab character" does switch the editor to tabs.
• Otherwise, changing "Indent" does change the number of spaces used when reformatting.
• If .editorconfig is present and enabled, it overrides the setting as expected (both indent_style and indent_size are obeyed).
• Editing, code actions, refactoring, etc do seem to obey the selected settings.