Apply advantage mechanic to all die and allow settings for users to set defaults

[zithith]

Is your feature request related to a problem? Please describe.
Currently our implementation of advantage isn't exactly right. The mechanic is more nuanced than the kh/kl modifiers. We need this to be handled correctly as the default, but allow user flexibility.

Describe the solution you'd like

• Take the work from Implement advantage dice picking functionality for plot die #231 and apply the custom modifier(s) to any die type
• Add settings for the user to select whether they default to kh/kl or picking with non-plot die, with the system default being to pick
• Update the roller dialog so that it can handle multiple [dis]advantages (only has to be one or the other) and spread them across d20, plot and damage die
  • Design suggestion before was to display the pool as a set of die icons.
  • Then you could click the icons to apply one of the advantages to that die.
  • [Zithith's Suggestion]: Still split the pool up by roll term - this will identify plot d6s from standard d6s in damage easier.
    • This then gives an alternative input for advantages by way of a number or slider input for each line (which may be simpler to manipulate in code).
  • There will need to be a max number displayed of advantages to apply. Possibly a counter: "X/Y applied".
• Add the relevant number of die to each part of the pool and use the custom modifier to prompt for the right number of picks per die term (or use kh/kl per the setting selection).
  • Note: whether it's the player or GM who picks for adv/disadv will change depending on who is rolling!
  • Though we still will just implement this as the player picking regardless of whether it's adv or disadv.
• Leave the shortcut modifier keys as they are (they can be shortcuts to just rolling the skill check as if it were a D&D check)

For 1.0 we will have to put up with multiple prompts appearing if the advantage is applied to more than one type of die term. If we can come back to it later it'd be great to try and amalgamate all the picks needed for a roll but I don't know if that's possible with roll modifiers.

If using the "click a die icon to apply advantage" approach then modifier keys could then be used here again to define if the user wanted it as "pick" or kh/kl. Implementing that isn't the scope of this issue though.