Check for proj4 in a way that also works in module environments
Merge pull request #2333 from ahocevar/better-proj4-check

Check for proj4 in a way that also works in module environments
Make attribution control collapsible.
Remove Logo Control from defaults
Remove Logo Control
Move Logos in attributions
Do not collapse Attributions when using OSM source
Register button handlers the new way
Add getter/setter for collapsed & collapsible
Add attributions example

Showing how to dynamically change collapsed/collapsible properties for ≠
map sizes.
Remove reference to ol-logo
Use @api annotation
Merge pull request #2159 from tonio/attributions

Merge Logo control into Attribution
Be stricter with the type of ol.source.TileWMS#_urls
Add tilePixelRatio option to ol.source.XYZ
Add ol.source.TileWMS#setUrls and setUrl
Merge pull request #2335 from elemoine/pixelratio-xyz

Add tilePixelRatio option to ol.source.XYZ
Merge pull request #2336 from elemoine/seturl

Add ol.source.TileWMS#setUrls and setUrl