Native overlay for switching input methods

## Problem

Currently the input method itself handles the overlay popup (such as with mozc) which doesn't fit the elementary style or level of design quality (it doesn't have a border, and images for methods such as mozc are low-res. etc)

The overlay also seems to have a mind of its own and doesn't update the indicator, making it impossible to judge what you're using (this is worthy of its own issue)

## Proposal

Disable the input methods own builtin keybindings and create a native one that is styled with the elementary design language. Probably with a popup bubble like volume and brightness, which would match their 'system' function.

## Prior Art