Add functionality for fallback emotes within Reddit

[Ebreium]

Introduces the ability to add a fallback emote on Reddit to increase compatibility for those without BPM.

This is done by entering a second emote as a modifier, which the BPM client then uses instead of the parent emote while a browser without BPM will render only the parent.
So [](/twibeam-/ktwicute) will render as twibeam for those without BPM, and ktwicute for those with the extension.
As the slash designates a modifier to be an emote, any other modifiers before or after the second emote are preserved, meaning [](/twibeam-i-/ktwicute-r) will appear as an inverted and reversed ktwicute for BPM users.

The click-toggle function was also changed in order to cycle through the full emote with all modifiers, the full text, and how a user without BPM would see the emote.
Example:

Uses:

• Allowing users who wish to have only a BPM emote present in the body of their comment able to do so while not appearing as a blankpost. For instance this is one such comment that could be fixed with something like [](/twisad-/sadlyra).

• General smoothing of emote usage from more innate integration with default emotes. Here is a comment made by Faranight using the feature on the main sub mainly to test, but it illustrates this nicely.

• Short RPs that often compromise variety for accessibility, such as most posts on /r/emotestories.

This was a joint effort by Faranight, ByzantineFailure, and myself.

[bb010g]

Could these be squashed? Also, your editor seems to have put tabs in.

[Shugabuga]

Also, your editor seems to have put tabs in.

To be honest, this repo has no real code style guidelines, so I doubt it matters. Worse case, someone can add a commit converting everything into spaces.