Add support for Vaadin 8

[mvysny]

Could you please add support for the now-released Vaadin 8? Having LQC compatible with Vaadin 8's v7.Grid would be awesome since it would allow gradual migration of the app using LQC towards Vaadin 8.

Thank you 👍

[mstahv]

There actually seems to be a PR already available: #100

[mvysny]

Tested this patch and found it to be working. Reviewed the code - OK.

[StefanPenndorf]

Supporting Vaadin 8 is great but might require to maintain two branches - one for Vaadin 7 and one for Vaadin 8. We're forced to stay at Vaadin 7 for some time (our customers do not admit that IE8, IE9 and IE10 are almost dead). Would be bad if bugfixes and enhancements would not be available for LQC with Vaadin 7.