[Feature] Provide a stat generation utility for the system

[Pjb518]

We should provide an interface for quickly generating a set of stats for a character, available only when the sheet is unlocked.

Given the wide variety of stat generation methods available, this interface needs to be flexible, and we need to provide a number of auxiliary settings. By default, we should provide:

• A standard array
• Point Buy
• Roll generated stats (default formula 4d6kh) with the option rolling stats in order or rolling 7 sets and dropping one.

In terms of settings we need to provide:

• The ability to disable any of the default modes.
• The ability to set a default select for stat generation mode.
• The ability to define a custom array.
• The ability to set the maximum value available via point buy.
• The ability to set a total point allowance for point buy.
• The ability set a cost value for each value when using point buy.
• The ability to set a custom roll formula for roll generated stats.
• The ability to lock the "roll 7" option on or off.
• The ability to lock the ordered rolls option on or off.