PROV-833 Removed duplicate views for XLSX search result export

There is no need for one view per table if the views are all the same
anyway.

Also added a couple of cell-size related tweaks to the export itself.
Still have to deal with media preview dimensions.
NOJIRA Added a import and HTMLPurifier DefinitionCache directories to global gitignore
PROV-833 Improved media version handling for XLSX search result export

Some of this code was taken from pr/76.

- calculate column widths and row heights from media dimensions (we can
do that for each row, it doesn’t slow down significantly)
- make sure we only insert actual media when rendering mode for the
display placement is ‘media’ (as opposed to ‘url’)
- make sure we only insert jpegs