Merge pull request gridstack#1608 from adumesny/develop

v3.3.0

Merge pull request gridstack#1592 from adumesny/develop

create placeholder divs on the fly

Merge pull request gridstack#1584 from adumesny/develop

rev 3.1.5

Merge pull request gridstack#1565 from adumesny/develop

rev 3.1.4

Merge pull request gridstack#1553 from adumesny/develop

rev 3.1.3

Merge pull request gridstack#1528 from adumesny/develop

v3.1.2

Merge pull request gridstack#1525 from adumesny/develop

web component fixes

Merge pull request gridstack#1517 from adumesny/develop

force typescript 3.6 as 3.7 has breaking change

Merge pull request gridstack#1494 from adumesny/develop

doc for v3 release

Merge pull request gridstack#1443 from adumesny/develop

setting margin option support CSS '5px 10px 0 20px' format