Unify sidebar and main view type

[ysmilda]

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From discussion #119 it became clear there is a wish to be able to use the different object types in any position.

The proposal is to

• Combine the sidebaritem and mainitem into one
• Combine the modals for both
• Allow to drag and drop items from sidebar to main and vice versa

This issue is made to work out a plan of attack as well as track the design decisions along the way.

[ysmilda]

The first steps have been set. I've merged the MainViewItems and SidebarItems into one modal. Next up is rendering them.

To do this we need to decide on how we're going to do that. I see the following options:

• Create a single Context.svelte which unifies the rendering of all types. Making the style selectable.
• Keep a separate Context.svelte for the main and sidebar. Keeping a set style for each position.

I prefer the first option as it is easier to maintain, and allows the user full control over the look and feel of the items. Any difference in look can then be made toggleable or set depending on position in the screen.

What are your thoughts on this @matt8707 ?