Updates to styling and reactiveness

[ajolipa]

In this PR

This PR does two main things.

• Instead of having the viewer be set to 100vw and 100vh, it now defaults to filling the width of its container. The goal of this is to make it easier for developers to include the Edition Crafter viewer in their page layouts in a flexible and responsive way.
  • As part of this change, I also updated the CSS to not hide the dropdown menu and help icon when at narrow widths. However, that feature could still use some better styling; right now it just wraps around and displays on the left of the pane when the width is small.
• This PR also adds a simple loading spinner to both the transcription view and the image view. The caveat is that the loading spinner for the image view only appears while the OpenSeaDragon viewer is first mounting; if the actual image inside the viewer takes a few seconds to load, there will still be a blank screen. I'm not sure how to make that behave differently without diving into the OpenSeaDragon code.

Further work

• As mentioned, there is still some refining of the layout on "mobile" or generally narrow widths. (For this it might be nice to know exactly what the desire layout is -- should the dropdown still be in the upper right? Should it be modified to be smaller or be hidden by default and revealed with some sort of little arrow or tab or something?)
• I have not yet added any sort of loading spinner to the Image Grid view.
• In general, this should be tested pretty robustly in various different layouts/sizes before this PR is merged; I'm sure there are some weird corner case layouts that I did not account for yet.

[NickLaiacona]

Found a couple of weird states here - easiest to test if you pull EC into its own tab:

[ajolipa]

Think it's looking better now; see what you think @NickLaiacona .