Introduce rowspan feature

[jarvisteach]

Add 4th positioning option - rowspan

Currently, appJar supports positioning in a grid cell by row/column, and also allows a widget to span multiple columns.

There should also be the ability to span multiple rows - this is supported by the grid layout, so is just a case of introducing it to all the add functions.

[jarvisteach]

Mostly introduced - can now pass 4th RCS parameter to all widget creations and seems to work fine
Containers are populating it (0), but it can't be set yet on a container...

TO DO: change startContainer functions to include rowspan

[jarvisteach]

TODO: sticky needs updating, we now want the ability to set a top/bottom (N/S) sticky, so that widgets fill rowspan
Maybe default widgets with a rowspan to auto stick to top & bottom?

[jarvisteach]

All containers now take rowspan

[jarvisteach]

Closing this issue.
New issue created to deal with sticky #41