Partly fix #405: Keyboard icon does not match theme
This commit makes sure that the ibus icon on the panel matches the theme. It does not provide a fix to the other half of the issue where the keyboard indicator doesn't match the theme. A fix for the same will be worked on for the next release.
The commit is required to achieve something rather than nothing out of the time spent on tracking down the root cause of the issue.
Side effects: No known side effects.