Polish up many of our settings forms.

Many of our fields that expect lots of text were very short, making it
hard to really input or read the contents. These fields have been made
much wider.

Some fields that didn't need to be as wide as they were were made
smaller. For example, some fields accepting small numeric values.

This also adds some consistency to the sections for our forms by
removing the "General" titles for the sections. Now the general settings
for a particular settings page are just listed under the setting
category (such as Diff Viewer).

Went through each form and made sure the fields seemed long enough, and
that all settings pages were consistent when it came to their sections.