Server settings improvements
This issue contains a list of improvements in the server setting area.

- [x] Add file storage support (upload and temporary/permanent file links creation), to be able to upload custom logo and reference it right from the instance
- [x] <strike>Server theme customization and other UI settings</strike> Move to #166
- [x] More server actions: server restart action
- [x] Possibly improve logs page UX for working with many log files
- [x] Add ability to re-configure server without running scripts (ssh to server and then running settings) ([configurator](https://configurator.bitcartcc.com) is out)
- [x] <strike>Add ability to dynamically configure instance domains and their corresponding components (allow installing multiple store POS, for example, or using one store POS on multiple domains at once)</strike> Has no practical use for now
- [x] Restart server management command
- [x] <strike>Custom scripts execution policies</strike> Moved, see #165