When loading a category, don't also create UI for the subcategories.
This is weird and doesn't make sense, and is also the reason we
needed the hacky NoRemovePanel.

Previously, we added a category, then created a new panel for
each of its subcategories. When you clicked on the subcat
we made it again with a new panel, and the component ended
up on both (because it couldn't be removed from the old one).

Trying to copy 0 chars from a line is silly and breaks things.

Also some minor tidying.

Fixes DMDirc/DMDirc#483

Don't auto scroll to selected error.
Don't update the whole row just for a cell change.

Reset scroll pane to 0,0 when changing error.
Add message to the details panel.
State what is what in the details panel.

PluginInfo randomly implements Comparable and compares itself
by name, which I want to kill.

Issue 281