Use CellReference instead of FlyweightCell in Grid APIs (#13334)

Change-Id: I519e433219a028e99678574227ca44d5b66d07bc
Add missing @since and @author to RendererCellReference (#13334)

Change-Id: I5b09993fd604ea20cfea685b56122cf55b88dce5
Use CellReference in Grid events and event handling (#13334)

Change-Id: Ie4ed85e56f0c23850eec56518a7493f5ed3257bd
Use CellReferences everywhere in Renderer APIs (#13334)

This patch adds getElement() to RowReference and CellReference

Change-Id: I3df6e50256f628e5cdb5d64d741ff1eb59e8e1c3
replace com.google.gwt.json.* usages with elemental.json.* (#8942)

Change-Id: I745b12685be4696fd8f1158005bf731f35ae8a81
Fixes an issue where IE8 refused to fire one scroll event (#13334)

Change-Id: Iaf9278a3a16360369fde5ac6d759e27e5c443d1b
Fix ClickableRenderers to use CellReferences (#13334)

This patch also uses row keys and column ids in communication rather
than indices.

Change-Id: Ie3bb554bd5c45700f1681160eef08bef8beeaaee
Missing @since for 7.4

Change-Id: I8fdf0c264febf2ab9ae0f230f6bb357ef57be9ec
Fix regressions in Grid SCSS

Fix regressions from previous Grid style patch:
- Typo in selector (dot instead of comma)
- “active” style renamed to “focused”
- Scrollbar border styling moved from Valo (was working) to Base (now
all themes work the same)

Change-Id: I778de73027f0cb9def1fb93e5188f494f0a49639
Merge remote-tracking branch 'origin/grid' into 7.4
Merge remote-tracking branch 'origin/master' into 7.4

Conflicts:
	server/src/com/vaadin/data/util/AbstractInMemoryContainer.java

Change-Id: I39b742a96653de3a59571b4e9b4143fd2e3d3978