[web] add calendar webview

.gitignore

internal/server/handlers.go

internal/server/server.go

internal/server/web/partials/navbar.mustache

internal/server/web/partials/scripts.mustache

...ver/web/partials/settings-notifications-calendar.mustache

internal/server/web/partials/style.mustache

internal/server/web/sites/calendar.mustache

internal/server/web/static/css/calendar.css

internal/server/web/static/js/calendar.js

...l/server/web/static/js/lib/fullcalendar-6.1.10/LICENSE.md

...al/server/web/static/js/lib/fullcalendar-6.1.10/README.md

...eb/static/js/lib/fullcalendar-6.1.10/dist/index.global.js

...tatic/js/lib/fullcalendar-6.1.10/dist/index.global.min.js

...b/fullcalendar-6.1.10/packages/bootstrap4/index.global.js

...llcalendar-6.1.10/packages/bootstrap4/index.global.min.js

...ib/fullcalendar-6.1.10/packages/icalendar/index.global.js

...ullcalendar-6.1.10/packages/icalendar/index.global.min.js

internal/server/web/static/js/lib/ical/ical.js

internal/server/web/static/js/lib/ical/ical.min.js