bugfixing glElementfactories
add IHasMinSize + check the element itself for matching during
getLayoutDataAs
 * start with simple Border factory
 * let the heatmap consider another option: forceTextures
 * let the heatmap just render the picking details upon request i.e. the
mouse is in the heatmap
HeatMapElement picking now based on computation instead of rendering, 
that means with textures -> just two rects are drawn for a heatmap
Merge branch 'develop' of git@github.com:Caleydo/caleydo-dev.git into develop