JS issues on XAR Import UI

1. If no file is selected there are multiples warnings displayed, instead of just one [warnings.png] (r26562)

2. IE6 - the interface display is the one when JS is off (the Select All/None does not appear) [IE6.png] (not an issue)

3. IE6 - if you deselect all files and press Import - all files will be importer instead of none + warning see XWIKI-4845 (not a JS issue)

4. If you deselect pages one by one, when no page is selected, the Space selector still remains selected [selection.png] (r26562)

5. Remove from JS the inline styles. They are not needed, break wcag.
5a. <div id="packagecontainer" class="" style="min-height: 200px;">
5b. <ul class="xlist" style="text-indent:0px">
5c. <li class="xitem xhighlight" style="text-indent:0px">

6. UX: the message should be modified. [message.png] This is not a document, is the wiki importer. User doesn't see this as attachments, but as packages. (done in r26629, even though not a JS issue)