Logo customization for single-user & multi-user modes (#186)

* implemented logo customization for single-user mode

* removing unneeded comments

* added dark and light mode support for default logo

* implemented dark and light mode switching in frontend

* fixed dark and light mode switching for failed to load logo from backend

* removed unneeded comment

* custom logos for admin implemented

* refactor logo mgmt functions
abstract logo management utils into their own file for simplicity

* added settings tab for appearance on single-user mode

* unchecking files with unneeded changes

* fixed appearance settings tab to be hidden on multiuser mode

* allow readall for logo

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Co-authored-by: timothycarambat <rambat1010@gmail.com>