Currently we have Archer and Maceman classes on the one hand, but Javelin and Spear. For consistency and to make things more straightforward for future additions, it would be good if classes match their templates, e.g. `template_unit_infantry_ranged_slinger.xml` has Slinger (and not Sling) class.
This patch:
* adds LandTrader to support traders
* adds NavalTrader to merchant ships
* removes Spear class from pikemen templates
* renames:
* Axe → Axeman
* Javelin → Javelinist
* Pike → Pikeman
* Sling → Slinger
* Spear → Spearman
* Sword → Swordsman
* corrects other simulation files accordingly
* updates the `components/Identity.js` file
[EDIT]:
* gave the gastraphetes a Crossbowman class
* gave the clubman a Clubman class
* Catapult → StoneThrower
* made Mechanical a non-visible class (cf. Human, Organic)
* made FishingBoat a visible class
* introduced Bireme, Trireme, and Quinquereme visible classes