OpenLayers optimizations

[fredj]

see #1544

Notes:

• The Infinity preloading applies to all WMTS layers, not only to the background layers.
• All the tiles are loaded while animating and interacting (but only form the desktop interface)

[sbrunner]

Looks good, but #1544 should steel be open (or create a new issue) :-)

[fredj]

Looks good, but #1544 should steel be open (or create a new issue) :-)

I've replaced fixes with see. The last point "Priorise the tiles downloading for the WMTS base layers" is not possible with OpenLayers: all the tiles are loaded with the same priority, it's not possible to have a higher priority by layer

[fredj]

@sbrunner I've not activated to preloading for the mobile interface to save the bandwidth, is it ok for you?

[sbrunner]

ok :-)

[fredj]

Thanks for the review