WIP plugins: load theme on client side

client/proxy.config.json

...config/edit-custom-config/edit-custom-config.component.ts

...nt-interface/my-account-interface-settings.component.html

...ount-interface/my-account-interface-settings.component.ts

client/src/app/app.component.ts

client/src/app/core/plugins/plugin.service.ts

client/src/app/core/theme/theme.service.ts

client/src/app/menu/menu.component.html

client/src/app/menu/menu.component.ts

client/src/index.html

server/controllers/api/config.ts

server/controllers/themes.ts

server/initializers/constants.ts

server/initializers/migrations/0400-user-theme.ts

server/lib/client-html.ts

server/lib/plugins/theme-utils.ts

server/models/account/user.ts

shared/models/server/server-config.model.ts

shared/models/users/user.model.ts