Proposal form improvements and Proposal drafts.

A recurring problem is writing out the proposal in Alchemy only to accidentally close it or click anywhere outside the proposal box for it to disappear. Considerable time has been lost on this and there have been several complaints recently from DXdao members.

> can you guys push a redesign of the proposal form? make it more confortable to work with longer proposals, the UX when we are submitting long proposals is terrible
> Yes, even a feature like draft proposals where alchemy can save drafted proposals in the browser localhost, and list them, darft and templates

The solution for this would be to save (autosave) proposals as they are being filled.

* Add a “save” button plus an auto save for the last proposal you were editing in a specific scheme / plugin
* Save the proposal to localStorage, specific to the scheme
* Prefill the proposal form for the said scheme with the saved proposal when the proposal form is opened.

Additional improvements
* Make the proposal form accessible without a web3 connection (obviously you can’t submit without it, but you should be able to write and save to it without one)
* Proposal form adjustments:
* make the description field of the proposal form expandable
* Use the competition submission layout for the proposal (sidebar entry)
* improve the preview UX (preview tab should only show the preview, right now it shows raw and preview without a dividing line?)