[FR] White labeling

[matmair]

This PR adds more customization options to Inventree:

• Add a message to the login page
• Add an info banner to the main page
• Exchange the logo
• Remove the InvenTree name from all user-facing places

Fixes #2301

[matmair]

@SchrodingersGat this will require slight changes to the demo instance: the demo texts were removed from the code-base and moved to the config template. Please just remove the comments on the new lines there and everything should be back as before

[SchrodingersGat]

Looks pretty reasonable, I'll pull it down and have a closer look.

Please also add a PR to the docs repo with:

• A brief rundown on the "white labelling" feature
• An entry into the release notes for 0.7.0

[SchrodingersGat]

Navbar Message

Navbar message alignment can be tweaked a bit, should match the current demo instance, centred vertically and horizontally

[matmair]

Navbar Message

Navbar message alignment can be tweaked a bit, should match the current demo instance, centred vertically and horizontally

@SchrodingersGat I have changed the template example to use h6 tags so that the size fits the current method. The result between the demo and this PR is the same now.
Also, the content is centred in the navbar.

[SchrodingersGat]

@matmair this looks great now, thanks for the updates. Can you add some documentation when you have the time?

[matmair]

@matmair this looks great now, thanks for the updates. Can you add some documentation when you have the time?

@SchrodingersGat PR is already in