Add island feature to grid

[thomaskrause]

The grid view should show "..." and a gap where tokens are missing between matches+context (#1, #2 etc.), just like in the KWIC view (eventually the tree should do this too)

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Imported from Launchpad using lp2gh.

• date created: 2011-06-19T14:33:00Z
• owner: amir-zeldes
• assignee: annis
• the launchpad url was https://bugs.launchpad.net/bugs/799428

[thomaskrause]

(by amir-zeldes)
The gap can be identified by a gap in sequential token index in the token stream

[thomaskrause]

New implementation of the grid will handle gaps by adding empty token, so this is fixed.

[pixeldrama]

This is linked with that #36 and not fixed.