Add comments for obsolete strings in translations

[Uwuewsky]

Summary

I18N "Obsolete strings now have a comment with an explanation"

Purpose of change

Objects in the game may be declared obsolete, but their text is still extracted into translations and these obsolete strings are hard to distinguish. The only hint is the file path (in the red box).

Describe the solution

Transifex apparently doesn't support syntax for deprecated entries from gettext, so replace the comment (in the green box) with a warning for those strings that only occur in obsoleted files.

1. A warning is added to lines whose file path has obsolet[e|ion] in it.
2. In the lang/update_pot.sh file, you can explicitly specify a substring via a new argument.
3. Manually added obsolete mods.
4. Added description of this feature in the documentation.

Describe alternatives you've considered

Remove obsolete strings from translations?

Testing

The translations are extracted successfully, the comment has been replaced only in the right strings.
Comment replaced for a line with an obsolete source:

#. ~ [DEPRECATED] Don't translate this line.
#. ~ This string is from an obsolete source and will no longer be used in the game.
#: data/mods/BlazeIndustries/recipes/blaze_construction_recipes.json
msgid ""
"Converts a fridge to run off of vehicle power.  You can 'e'xamine it "
"afterwards to take it down for mounting."

Comment replaced for a string with multiple obsolete sources:

#. ~ [DEPRECATED] Don't translate this line.
#. ~ This string is from an obsolete source and will no longer be used in the game.
#: data/json/obsoletion_and_migration_0.I/gun.json
#: data/mods/Generic_Guns/recipes/recipe_obsolete.json
msgid "PPSh-41 submachine gun"

The string is used somewhere else, the original comment remains:

#. ~ Name of body part
#. ~ Mutation name
#: data/json/body_parts.json
#: data/json/obsoletion_and_migration_0.I/prosthetics.json
#: data/mods/Limb_WIP/mutations/mutations.json
msgid "right arm"

Additional context