Cache icons trough starts

[DeathsGun]

Is your feature request related to a problem? Please describe.
Currently every time ModManager is started and the UI is used it downloads the icons and only holds them in memory.
This should be changed to a small cache which stores the icons between starts.

Describe the solution you'd like
A directory under mods/ModManager/icons which contains all the needed icons.
If the icons get over specific MB amount the oldest images get cleared

Describe alternatives you've considered
Removing items after a specific amount of time