Small improvements in update site table

[NicoKiaru]

1. The description column editability should be set to false (very minor)
2. Ideally, we could try to render markdown url links in this description column, and potentially use a PlatformService to open a navigator window when a user clicks on the link.
3. Make the window maximizable
4. Be able to increase more conveniently the description column (it's a bit painful currently), and potentially multiline (not completely sure it's a good idea) (ping @tferr)

[tferr]

I would add a couple more:

5. Make the size of updater dialogs a persistent preference: I had to run the updater on a Mac one of these days and the dialogs were always reverting to some unreasonable size

6. Add a 'last modified' column. That would help to figure out 'less active' sites.

Comment on 4:

Be able to increase more conveniently the description column (it's a bit painful currently), and potentially multiline

I had messed around with JTable#setAutoResizeMode() and could not get reasonable behaviors out of it. I probably don't understand how it works. I find column resizing in swing tables in general quite clunky. Also, I guess from a UI point of view, the most appropriate would be to display the description on a right-hand side tab (similar to the "Details" tab in the main updater dialog).

The host and Directory on host columns could probably go toward the end of the table.

Unfortunately, I won't have time to look into it.