feat(favourites): add, edit, import and export of favourites

[nijuyonkadesu]

Is your feature request related to a problem? Please describe.
Currently, there is only one way to save fav images, ie, to download the image itlsef to 'Pictures' directory. Having and exporting urls would be nice? (✿◡‿◡)

Describe the solution you'd like

1. Add
   
2. Edit
   
3. Import
4. Export
   

Describe alternatives you've considered
Minor additions to above feature:

• Do we need a batch download on these URLs ?
• A toast with a small img thumbnail? (coz, the image selection mechanism is not super accurate in SAO)

maybe, just maybe ~
navigate to another carousel view (vertical), but show only the favourited urls?
with a heart icon (spam it)
with a delete icon (ofc) + undo snack bar

[nijuyonkadesu]

this and #17

[nijuyonkadesu]

plan is to simply store them as list

• it would be nice to group favourites under various categories
• map with emoji? feat(stickers): foundations for a dynamic sticker app #21

^^^^ will plan out when window manager thingy is figured out

[nijuyonkadesu]

auto categorize with ML model?
ehhhhhhh

[nijuyonkadesu]

actually I want SAO to be the alternate repository for stickers that work on all applications ~

[nijuyonkadesu]