#1 fixed.

Implemented the following behavior:
When I do a clean install the Destinations->Image uploader->Imgur is checked, but Destinations->Image uploader->File uploader->Dropbox is not checked.
If I click on items inside Destinations->Image uploader->File uploader then the behavior must be as is, that is Destinations->Image uploader->File uploader must be checked to show me that item inside is selected.
Now if I click on items inside Destinations->Image uploader other than File uploader then all items inside File uploader must be unchecked to avoid misleading me.
If Imgur is selected and I click on Destinations->Image uploader->File uploader then some item inside must be checked automatically. If there was previous selection then it must be set. If there were no previous selections than first item in the list must be checked by default.
#2 fixed.

fixed the same way as #1.
Merge branch 'master' of https://github.com/barsv/ShareX