Cell spacing fix

Added the html constant space rather than a text space to enable
multiple spaces per cell

issue: A24Group/Triage#3520
Merge remote-tracking branch 'upstream/master' into textColumnSpacer
Added the code to customize the style for a header

issue: A24Group/Triage#3520
Merge remote-tracking branch 'upstream/master' into textColumnSpacer

Conflicts:
	src/org/ssgwt/client/ui/datagrid/column/SSTextCell.java
Added the a24 licence and the class docblock
Fixed the last CS tab
Merge pull request #201 from michaelbarnard/textColumnSpacer

Cell spacing fix and custom header styles