Get rid of default browser prompts and dialogs

[begedin]

This is a catch-all task used to keep track of every place in the code we're using a window.alert, window.prompt or window.confirm. Ideally, we would eventually replace these with actual UI controls of our own.

It's in the backlog and depending on how simple or complex each individual case is, additional tasks may be created.

Places we're using window.alert() in:

• components/share-modal upon error during permission creation
• components/share-modal upon error during permission deletion

Places we're using window.confirm() in:

• components\share-modal upon permission deletion, to ask the user to confirm

Places we're using window.prompt() in:

• lib/document-source in createFromState to prompt for document title