Add a user preference to select the location of an edition opened from a concordance

BP note:

Opening the Edition view alongside the concordance view is more convenient for me :

computer monitors have got more room on the side than above, because of their wide shape (16:9)
TXM current default editions are often portait-oriented
it is less useful to see the complete concordance line (with large contexts) when Edition is displayed because the full-text edition provides large contexts as well.

see: “Edition\Preference\Edition\new editor position” and play with the values and the double click from concordance line to edition command
validate and translate the preference name
decide which value should be set as default in TXM (actual is equals to “ABOVE”)

(from redmine: issue id 2733, created on 2020/01/22 by Sebastien Jacquot)