Navigation improvements

OAuth tidy-up and refactor

This uses the main navigation bar for the Customize and Stats pages, instead of the collection-navigation bar used for multi-user / multi-collection instances.

This makes it easier to navigate between different blog sections: Customize, Stats, View.

This includes the platform mark with each login button and uses
brand colors. It also uses the same style on the Account Settings
page. And it wraps buttons on login / signup pages.

This updates signup.tmpl to include all supported OAuth methods and respect the new `DisablePasswordAuth` config value.

This moves fields into the `OAuthButtons` struct and puts the buttons into templates/includes/oauth.tmpl.

Previously, these display names were swapped.

Login with generic oauth feature++

Support AP-style mentions of centralized social media accounts

This adds support for mentioning profiles on the following sites:

- deviantart.com
- facebook.com
- flickr.com
- github.com
- instagram.com
- reddit.com
- wattpad.com
- youtube.com

Use a bigger font size for h2

Added Gitea OAuth login and account management.

Add menu hover delay

Mathjax in binaries

Dark mode pad

Support post signatures

Ref T582

Bump github.com/fatih/color from 1.7.0 to 1.9.0

Bump github.com/manifoldco/promptui from 0.3.2 to 0.7.0

Bumps [github.com/fatih/color](https://github.com/fatih/color) from 1.7.0 to 1.9.0.
- [Release notes](https://github.com/fatih/color/releases)
- [Commits](https://github.com/fatih/color/compare/v1.7.0...v1.9.0)

Signed-off-by: dependabot[bot] <support@github.com>

Bump github.com/go-sql-driver/mysql from 1.4.1 to 1.5.0

Bump github.com/guregu/null from 3.4.0+incompatible to 3.5.0+incompatible

Bump gopkg.in/ini.v1 from 1.55.0 to 1.57.0

Bump github.com/urfave/cli/v2 from 2.1.1 to 2.2.0

Bump github.com/writeas/import from 0.2.0 to 0.2.1

Bumps [github.com/urfave/cli/v2](https://github.com/urfave/cli) from 2.1.1 to 2.2.0.
- [Release notes](https://github.com/urfave/cli/releases)
- [Changelog](https://github.com/urfave/cli/blob/master/docs/CHANGELOG.md)
- [Commits](https://github.com/urfave/cli/compare/v2.1.1...v2.2.0)

Signed-off-by: dependabot[bot] <support@github.com>

Bumps [github.com/manifoldco/promptui](https://github.com/manifoldco/promptui) from 0.3.2 to 0.7.0.
- [Release notes](https://github.com/manifoldco/promptui/releases)
- [Changelog](https://github.com/manifoldco/promptui/blob/master/CHANGELOG.md)
- [Commits](https://github.com/manifoldco/promptui/compare/v0.3.2...v0.7.0)

Signed-off-by: dependabot[bot] <support@github.com>

Bump github.com/stretchr/testify from 1.6.0 to 1.6.1