feat: display possible foci

also added a basic test character to the data/test-char.json file.
chore: use an Either for parsing the Character from JSON
feat: add JSON import/export
chore: add beginnings of foci

Going to introduce the ability to import/export work before I finish
this off. Import/Export will allow me to make changes to the JSON of the
character sheet easily, and to ensure that I can try out some test data
easily too.
feat: add backgrounds
feat: include XP until next lvl
feat: add ui to set attributes manually.
feat: add attributes and initial roll
chore: update class dropdown
chore: add attribute data

TIKT-123. Describe change further, add context and reasons for decisions.
docs: update readme etc
feat: add basic styles for xp and level boxes
chore: update build script

build script now cleans dist folder before adding more files
chore: add css, save every xp change
chore: remove practice files
feat: render level and allow xp to change
chore: initial commit