[fix] #731915 use add_onload instead of plain <script> tag for progress bar.
This changeset fixes : #731915: missing inprogress style on the project page
Content fetched with ajax have their <script> tags removed. (see #734414) We
now use the _cw.html_headers.add_onload method to execute the javascript code
necessary to draw the progress bar.
In the process we removed the ProgressBarWidget and merged it in
ProgressTableView.