simplify sentence [copyedit]

what it says on the tin.
Owner: catch ImportError in a less confusing, friendlier way
Owner: improve error on loading missing plugins
Owner: update error messages
s/This plugin is incompatible/This plugin may be incompatible/
Merge pull request #892 from GLolol/notify-incompatible-plugins-on-load

Owner: catch ImportError in a less confusing, friendlier way (Closes #861, Really closes #850)
Misc: default listUnloadedPlugins & listPrivatePlugins to False
Debug: Fix __init__.py for Python 3 compatibility
Merge pull request #898 from GLolol/debug-python3

Debug: Fix __init__.py for Python 3 compatibility
Merge pull request #897 from GLolol/patch-1

[suggestion] Misc: default listUnloadedPlugins & listPrivatePlugins to False