Extend selection data to contain the height of lines

The height of the lines at the start and end of selection is needed
to properly place selection handles. E.g. in SailfishOS design
they need to be positioned vertically centered on the line.
Merge pull request #53 from tmeshkova/extend-selection-data

Extend selection data to contain the height of lines
[embedlite-component] Extend selection data. Merge remote-tracking branch 'origin/master'