Blocks: Dotted border on hover and always show the placeholder

[youknowriad]

closes #1209
closes #1250

I've used "outline" instead of "border" for the block borders to avoid a flickering effect when the border size changes.
I tried the other option (using a margin to compensate the border size, but I've found the outline method way simpler even if theoretically it's less performant).

[jasmussen]

Thanks for trying this. I think I like it. But I'd like to ... hmm... sleep on it? Maybe get some other eyes on it? @melchoyce what do you think?

[melchoyce]

Can someone take a quick screencast/gif? I don't have the development version of the plugin set up.

[aduth]

@melchoyce : https://cloudup.com/clKQ5O_F4Ps

(The borders appear very very faint)

[melchoyce]

Thanks @aduth. Pretty hard to tell – I think I'll have to try it out for myself. I'll try to get the plugin setup.

[melchoyce]

Okay, had a chance to test this out. I... also think I like it? I don't love going from 1px on hover to 2px when active, but the dotted border doesn't look good at 2px, so maybe it's fine. I guess I'm a little ambivalent.

[jasmussen]

It sounds like we both like the idea of a border around the whole block, but that the specific design of it needs a little more time in the oven.

Let's keep this one open, tag it "Design", and think about a good design for it. Might be worth looking at desktop apps for inspiration.

[jasmussen]

Per some discussions in #130, we might want to put a couple of buttons on the right side, as a counter to the movers. In that mockup, an outline all the way around on hover is extra important. Here's one that just has a 1px solid border instead:

Here's a selected block:

[youknowriad]

Updated this PR with solid borders, we should leave the buttons for a separate issue.

[jasmussen]

I like it, I think we should merge it and then see if we need to revisit. Thanks for working on this. 👍 👍