cog geotiff support on wegue

[pvgenuchten]

COG support was introduced on openlayers in v6.7
@JakobMiksch has prepared a PR with migration to v6.7 at #261, which is a prerequisite for this work
What is the status on this migration?

I'll have a look at the build failures, to see if i can progress the work

[JakobMiksch]

@pvgenuchten I started this PR to try COG functionality, but had problems with upgrading OpenLayers. Then I switched to a "vanilla" OpenLayers (without Vue) to test COG. The PR #261 was just the outcome of my tries. Maybe meanwhile, with a newer OpenLayers version, the upgrade problems can be solved easier.
Any further progress on this would be much appreciated.

[pvgenuchten]

did a bit of research, the issue seems the use of older versions of webpack/babel in this project, because geotiff.js applies some recent js conventions. Updating webpack/babel seems not very obvious...