dock: Do not toggle window on clicking dock.
dock: Do not toggle window on clicking dock.

We are reverting back our decision after getting a lot of feedback
on this behaviour. Fromm now on, when you click on the dock icon we'll
show the app window and won't hide it after clicking again on dock.

Fixes: #914.
zulip/zulip-desktop,zulip/zulip-desktop,zulip/zulip-desktop,zulip/zulip-desktop