Easier entry of previously-used WMS addresses

[jeremyboggs]

After adding about three different Omeka items, each pointing to the same WMS address, it seemed it would be useful to select a WMS address from a pre-populated list instead of having to enter it each time. I could think of several different ways this would work, with each having repercussions for how the data would get entered. But I wonder if this workflow is common enough to account for in the plugin?

If anything, we could see about changing the input element for the WMS field from a textarea to a text input, which would allow you to cycle through that inputs history in the browser. Since we only expect one value here anyways, the textarea is unnecessary, though I think Omeka uses this by default.