Add ability to set custom alternate animation suffix

[r6915ee]

This pull request simply adds the ability to set the alt. animation suffix. As part of this:

• A new flag was added, DEFAULT_ALT_ANIM_SUFFIX, that sets the default suffix for alt. animations. By default, it is set to -alt in order to retain compatibility.
• A new property for StrumLine was introduced, that being defaultAnimSuffix, which is used to replace the suffix per-strumline. By default, it is set to the DEFAULT_ALT_ANIM_SUFFIX flag mentioned above.
• Alt Animation Toggle will automatically make use of the property above.

This change is primarily intended to technically allow for much more alt. animations on a single character without going through the process of a complete character change, thus acting as a more performant variant of theoretically "switching" characters.

Do note that, although the Alt Animation Toggle event has been updated to take advantage of the new per-strumline property, it did not receive any changes to allow setting the suffix directly as that is outside of the scope of the pull request (at least, in my opinion).

[r6915ee]

Now that I think about it, I'll probably add support for prefixes as well, as it makes sense like with the window titles. I'll put it back as a draft pull request for now and then convert it once I've made the change. (I'm not renaming the branch for this, I don't want to remake the pull request.)

[r6915ee]

Okay, there are some issues with events in particular (recycling appears to be definition-dependent in terms of parameter location) that prevent the easy implementation of prefixes. As a result, I'll ready the pull request for review again in its current state, but in my case I'll keep the animation prefix feature in mind; I have some ideas on how to implement that, alongside a potential backward-incompatible rewrite to the character animation system, but those are outside the scope of this pull request at the moment.