Update plugin to Spyder v4

[jitseniesen]

Currently the plugin fails in Spyder v4 with:

    from spyder.plugins.configdialog import PluginConfigPage
ImportError: cannot import name 'PluginConfigPage'

[Landau1908]

I meet the error, too.

[jcox-nd]

Did PluginConfigPage simply get renamed or relocated in Spyder 4.0? By doing a search of spyder origin/master, I find:
from spyder.api.preferences import PluginConfigPage

So what happens if you just change all references from:
'from spyder.plugins.configdialog import PluginConfigPage' -> from spyder.api.preferences import PluginConfigPage

Does it work?

[ccordoba12]

@jcox-nd, that's almost the right fix. You need to do something like this:

try:
    from spyder.plugins.configdialog import PluginConfigPage
except ImportError:
    from spyder.api.preferences import PluginConfigPage

to make the plugin compatible with both Spyder 3 and 4.

Please make a PR with that fix so we can release a be version.