Updating openlayers to v6.4.3

[simonseyock]

ExtJS components in openlayers controls and overlays do not work out-of-the-box as the click events get swallowed by openlayers. This is fixed in openlayers v6.4.3.

Because of this I looked into updating the openlayers version and took some first steps in #651

It seems pretty straight forward and I hope I will at some point get the time to complete this.

[enorton]

@simonseyock I've got your pull request checked out and so far 6.4.3 seems to work. I was wondering what else was on the to do list for this. I'm fairly new to geoext and openlayers so I'm not sure what to look for.

[simonseyock]

@enorton As the releases v5.0.0 and v6.0.0 contain breaking changes I was going through the upgrade notes in
https://github.com/openlayers/openlayers/releases/tag/v5.0.0 and
https://github.com/openlayers/openlayers/releases/tag/v6.0.0
I was currently at the point 'Removal of optional this arguments.' of v5.0.0 which is probably the change which caused the most code updates.

[simonseyock]

I wrote back then in the above linked issue in cpsi-mapview:

The only thing that I think is a little more work is the overview map - it can no longer show all parent layers but needs it's own layers.

[simonseyock]

https://github.com/geoext/geoext/releases/tag/v4.0.0