Distribute WebUi space using flex layout

[jevenski]

• Resize category list, torrent list table and torrent detail tabs using flex-basis property. This reduces the amount of JS doing resizing work and lets CSS take over the space distribution.
• Add a deprecation warning for the old theWebUI.resizeTop(w, h) method and suggest using the new simplified theWebUI.resizeTop(h) method.
• Fix an error that occurs when traffic graph is shrinked down to less than 1px high.

Fixes #2817

[jevenski]

This patch also fixes this issue mentioned in an early feedback for v5.0.

I also found that clicking on certain tabs in all the other themes causes the whole bottom section to grow vertically by 1 or 2 pixels. The tabs that do this the most often are the history and plugins tabs, but it happens with others depending on the theme. (Incidentally, this doesn't happen in the MaterialDesign theme.) I thought that it might be caused by the content of the active tab having x-overflow content, which could cause the scrollbar to appear and maybe bump the tab upward. But it happens even if I make the various fields in each tab narrower so that everything fits on the screen, so I'm not sure what's really making it happen. This isn't a big usability issue or anything. It's just a quirky UI thing where I can see the tab bar moving slightly up and down as I click through the tabs.

Originally posted by @Airman8 in #2721 (comment)

[stickz]

@jevenski This will be the next pull request merged. Afterwards, we need a hotfix for all platforms on v5.1 (without the deprecation). There's an issue when I take my web browser out of maximize mode. The traffic graph does not update.

[koblack]

Toggle details [F6] does not work correctly.
After pressing [F6] only the contents of the tab are hidden but this part of the window remains visible.

Screenshot:

[stickz]

Thanks @jevenski. I'll tag ruTorrent v5.1.4 once this is backported for a hotfix!