[feature] Added light/system theme

[alindt]

Added a light theme; not complete/optimized yet, but it's a start.

Fixes #412

[heisbrot]

Hey @alindt,

Thanks for your contribution!
Light mode is definitely needed and requested by many users.

I will look at your PR and see what we can do to push it for an initial version.
Probably will also need a "Beta" badge for it.

[markcst]

Hey @alindt,

Thanks for your contribution! Light mode is definitely needed and requested by many users.

I will look at your PR and see what we can do to push it for an initial version. Probably will also need a "Beta" badge for it.

Hi, @alindt , any news about it?

[daidi]

Hey @alindt,

Thanks for your contribution! Light mode is definitely needed and requested by many users.

I will look at your PR and see what we can do to push it for an initial version. Probably will also need a "Beta" badge for it.

any news? @heisbrot