some QoL improvements and fixes, nothing all too major. all in a day's work

CHANGELOG

- fix flaky image sizing (no more ballooning images)
- pixel art now renders with crisp edges (perfect for e.g. 88x31 badges)
- add arrow navigation in emoji picker
- focussing an emoji in the picker is now much more visible than before

- added limit to how many emojis get loaded at once (plus a "load more" button)
- lots of optimizations
- fixed resulting email sometimes containing stray empty image tags
- fixed uppercase/lowercase sometimes messing with alphabetical order
- load emojis as soon as the popup gets opened
- show error message in emoji picker if no emojis have been added yet