Add ability to mark modules for sale

[DarkFenX]

Use-case: few people might have vast inventories of rolled modules, but they might not care enough to estimate price and sell them, or do not want to spend ISK on contract fee, or might have too few contract slots. They might log into mutaplasmid.space, mark modules in their personal inventory as "for sale", and then such modules would show up in searches (if "negotiated sale" tick is chosen in search options). Search would show character-owner for such modules, so that person who seeks for this module can contact owner ingame.

Example would be Dark Magni, he sells his modules via unspecified broker for a hefty share. Just marking his modules and waiting for offers would simplify situation alot (as well as would put more rolled modules onto market).

Few additional thoughts:

• seller might avoid specifying price, specify exact price (+ put a mark that price is negotiable), or price range (same, could put a mark that price is negotiable)
• to avoid keeping entries from inactive characters, remove "module is for sale" flag for characters which haven't logged into mutaplasmid.space for 30+ days
• maybe worth to allow seller to specify another authenticated character as contact point
• once module changes owner, "for sale" flag is removed
• seller should control if location of the module is exposed or not, and maybe to what extent (region/system/station)