Add "EBU-N19" (*.stl) support

Issue : none

!! WARNING !!
Text position behavior changed :
- The old reference used the DCSub interop system (ref = text baseline)
- The new reference used the DCSUB smpte system (top, center, bottom
of text - relative to the text algnment)

"EBU-N19" support
- Import "EBU-N19" (*.stl)
- Export "EBU-N19" (*.stl)
- Display white, orange, red text edit border in function of the number of
characters ( <, =, > maximum characters per line)

Other changes:
- When aligned "top", the current line does not move and the new line
appear bellow.
- When aligned "bottom", the current line move above and the new line
- Add text background color support

Signed-off-by: juiice <decaen.julien@gmail.com>