Player Effects Module

Adds the playerEffects module to manage consumable functionality. Each consumable's "use" function has been replaced with a "consumable" table that includes the effect type and any other necessary values.

Additionally, using a consumable now displays a message on the HUD indicating its effect and, if it is a timed buff, will also show another message when the buff expires.

Note: Consumables saved from previous versions will trigger the "incompatible with playerEffects module" error in item.lua. ~~We could let these items fail silently and simply inform players that any currently saved consumables will have no effect, but that doesn't seem like an ideal solution. Thoughts?~~ I changed it to display a message in the HUD, rather than causing an error.

Added and cleaned up flashing functionality from #2048. Many thanks to @edisonout for her work.
Closes #1796 

Should fix #1975 but more testing is required to confirm.