Add all global sets, category groups, user fields, and asset sources, plus settings for each field

[danieltott]

This is sort of a large change, but this adds the ability to see field layouts for all of the available places you can add fields.

Also, added the ability to display field settings on a per-section basis. This allows easy access to things like dropdown options, or any other settings.

[jmuspratt]

@danieltott A year late, but I'm taking a look. In this PR I see encoded HTML getting output, so it actually renders as

Settings:
placeholder:    <em class="empty">none</em>
maxLength:  <em class="empty">none</em>

in the page. I tried adding the |raw filter in the _fieldsettings.html template, but that didn't fix it. Any ideas?

[danieltott]

@jmuspratt Hey! Yeah I think they changed the way they output things at some point - anyway wrapping those ternary operators in parentheses and then using |raw seems to have worked.

Unfortunately I don't have time today to try to merge this with some of the other changes that have come in but maybe next week I could look at it?