Hotkey conflicts with usual input method hotkey

[Cris Dywan]

The default hotkey Ctrl+Space conflicts with SCIM, which has the same by default. So Synapse will silently not come up if SCIM input methods are enabled.

Possible solutions I can see:
- Synaptic is brand new, it might be easiest to choose a different default hotkey
- Provide two default keys.
- Display a big warning that something else uses the same hotkey. Though this means all users of SCIM and Synapse have to customise hotkeys to use both normally.
- Display a big warning, provide a second hotkey, suggest the second hotkey.

[Alberto Aldegheri (albyrock87)]

We will display a "big warning" :)

<super>+space can't be used because some keyboard doesn't have the super key
<alt>+space can't be used because it's used in a lot of Window Managers