core: frontend: support "sponsor" logos

### Current behaviour

The BlueOS web interface is currently not very configurable, which is potentially problematic for companies selling their own vehicles based on other things together with BlueOS, and for users sharing content who want to represent and/or have quick access to sponsoring companies and organisations.

### Expected or desired behaviour

Beyond general theme components (like the colour palette and primary logo), it could be useful to provide a mechanism for specifying a set of logos (e.g. of companies whose technology is helping to power a vehicle). I envisage this being a set of logos that appears below the BlueOS Version information in the sidebar.

- The primary value is in being able to display logos
- I expect this could be achieved by having a set filename structure, and some form of consistent place or structure for where to find the files
- "Theme" type extensions should be able to provide a set of logos
- It may be relevant for other extensions to be able to provide a logo, and potentially have a corresponding user setting as to whether it is displayed (e.g. for the logos of device manufacturers)
- If someone has two extensions trying to add the same logo, it should automatically only add once (perhaps by using the same filename, even if they're in different places)
- There could be additional utility if the logo has a tooltip with some relevant information and/or acts as a clickable button that goes to a relevant organisation (or support) webpage

### Prerequisites

- [X] I have checked to make sure that a similar request has not already been filed or fixed.