Improve data entry ui

[cmho]

Closes #255. Closes #253. Closes #169.

this got... to be a lot, also there's a LOT of database schema changes. there will maybe need to be some database editing once this goes live to ensure stuff gets hooked back together, but also that can now be done in the admin UI now :v

[sublimemarch]

Error I get when I try to run this code.

[sublimemarch]

• Create documentation on how making new powers and power groups works. Consider adding help text.
• Add help text for "Allowed Ratings" in merits. Should it be [a, b, c]?
• When making a new flaw, I can't select the character type dropdown.
• Add help text to new character type form. Perhaps examples like Power Stat (example: Blood Potency)
• Error when loading character/new:

[sublimemarch]

Feedback for help text:

On /admin page:

• Rename "Character Types" link to "Creature Types." In general, this is what we should display to the user.
• The example of "Circle of the Crone Rituals" in "Power Types" is incorrect. They are a power group within the power type "Blood Sorcery". (according to Mark)

On /power_types:

• What does a status of "true" mean?
• There's another "Create New" button at the bottom of the page.
• On the new/edit form, change the "Character Type" select from a multi-select box to check boxes.

On /power_groups:

• On the new/edit form, what does "Active?" mean?
• On the new/edit form, change the select form to radio buttons. Should these also be alphabetical for ease of use? You should only be able to select one power type.

On /powers:

• On the new/edit form, change the select form to radio buttons. Make these alphabetical, and ideally give them unselectable headings of power type (it looks like they're grouped that way right now). You should only be able to select one power group.

On /merits:

• Add helper text explaining what specification and description mean.
• Should users be able to create new merit categories?

On /flaws:

• On new/edit form, why are there both a "Description" box and a "requires description" checkbox?

In general, we should change "true/false" in the active/specification/description column to "yes/no" so humans who aren't us can read it easier.