Make app state persistent between reloads

[pitkes22]

When a user returns to the page, the app should remember the state and should let the user continue the work.

Options, Channels structure, and image URL (if used to load an image) should be persisted in localStorage.

Caching of the uploaded image may be difficult due to the size limitation of the localStorage. One of the solutions I am thinking of is to use ServiceWorker for that but it needs research if this could be really done.

[BerndSchmecka]

In #11, I added Options and image URL (not channel structure yet) to localStorage. Since I'm more a Vue.js than a React guy, I'm not sure if my code is 100% efficient, but from my testing it works