Fix main menu alignment.
Added "f_standing_tank_w" entry
Added forgotten comma
Updated name of "f_standing_tank_w"

Changed name of "f_standing_tank_w" from "standing tank" to "standing water tank" to reflect the fact that it is restricted to holding water.
Updated tags for "f_standing_tank_w"
Added construction recipe for "f_standing_tank_w"
Updated "f_standing_tank_w" to "f_standing_tank"

Realized that the functionality was already in place for the wooden keg, so just needed to rework the entry to use the "keg" examine action instead of the "reload_furniture" one. This also allows the use of liquids in general, rather than just water, so that functionality has also been added.
Updated construction recipe for standing tank.
Updated standing tank entry

Balanced the standing tank to be better than the wooden keg, but require the appropriate amount of materials.
Updated yields from the standing tank
Updated iexamine::keg

Updated the iexamine::keg function to add the ability to set different volumes for different furniture. Currently this is determined by a call to the static method get_keg_cap, though that functionality should probably be moved into the furniture JSONs at some point, especially if we want to start adding more than a few types of "kegs".
Moved entry for standing keg to be in a sensible location
Updated get_keg_cap function

Increased the amount held by a standing tank to more accurately reflect the usage of the component tanks. That is, combining four together to get 900 volume means you would have somewhere in the ballpark of a quarter of the material left over - essentially another tank. This means the tank is actually somewhere around 1125, which rounds up to somewhere around 1200 due to surface area not scaling linearly with volume. A more precise value could probably be determined for this, but 1200 is somewhere in the right ballpark and is convenient because it simply and neatly doubles the already-extant wooden keg's volume.
Balanced standing tank

Made standing tank easier to construct to reflect the fact that you are using essentially ready-made materials. Also removed the wrench requirement and replaced it with the metal saw requirement that was previously intended.
Updated standing tank

Now requires hammering level two rather than hammering level one.
Added forgotten comma. Again.
Merge branch 'main_menu_tweaks' of https://github.com/yobbobanana/Cataclysm-DDA into merge2
Welder note.