widget based management instead of theme based

[Viko Adi Rahmawan]

now conky manager manage widget based on theme, but i think it would be better if enable/disable management are based on widget. The advantages are:
1. we dont need to enable all widgets on a theme when clicking a theme like happen now
2. widget management will behave like android one,
3. the edit and theme tab can be merge

i also suggest to have per widget preview file instead of per theme, the advantages are:
1. if theme package use per-widget preview file instead of per-theme preview file, we can have a nice widget selection like android.
2. one day if You want to make WYSIWYG location editor, You can use each preview file as object .

that are my idea, i hope you can take it into consideration for the next release, so far you did a great job. Thanks for your attention.