[FEATURE] Better emails

[jdabtieu]

Is your feature request related to a problem? Please describe.

Current emails are very bland. Accounts-related email (e.g. register, password reset) are very bland. When notifying participants of a contest, styling is not enabled either.

Describe the solution you'd like

Emails should look better & more professional. Additionally, some sort of basic styling should be enabled for announcement emails

[slightlyskepticalpotat]

HTML emails are supported with the current email plugin.

[slightlyskepticalpotat]

Breakdown of what needs to be done for myself:

• Rewrite emails to sound more professional
• Convert to HTML emails with website theme
• Test all of the emails work, ideally in CI too