Change default thumbnail size

[scolapasta]

For the upcoming dataset page redesign, thumbnails will be displayed in a larger form. However, the currently created thumbnails don't scale well to this new size. This issue is to:
• change the size for which thumbnails are created to 140x140 (@TaniaSchlatter please verify this the size we want)
• regenerate existing thumbnail

[scolapasta]

Note, we will eventually want the ability to produce thumbnails of different sizes (see issue #5679) but this is a smaller, quicker chunk to unblock this aspect of the redesign.

[pdurbin]

I just pushed 17c3891 to change 64 to 140 and here's a visual of how a dataset page looks:

Note that the trees next to the title are as small as ever. The trees in the file listing (and the other file) are now 140 pixels wide and covering up the file name.

I'll probably jump in #dv-design for clarification of what's desired.

[mheppler]

Added max-width:64px; max-height:64px; to the stylesheet in order to apply size dimensions to the file thumbnail on the dataset pg (file table), upload/edit files pg, replace file pg.

[mheppler]

Had a good call with @pdurbin to move this issue forward, which ended up being an unintentional code review.

Recommended changes include:

• revert CSS fix that I added for resizing the thumbnails images in the file table on the dataset pg
• revert image size change added to DEFAULT_THUMBNAIL_SIZE on ImageThumbConverter.java
• add new 140px image size to ImageThumbConverter class on ImageThumbConverter.java
• change dataset pg related (DatasetWidgetsPage.java?, DatasetUtil.java?) DEFAULT_THUMBNAIL_SIZE references to to point to new 140px image size instead

Would then like to discuss with the team (tech hours?) + @djbrooke if we should move these changes to my branch in order to apply the necessary UI front-end/css changes required to support this larger dataset thumbnail image, or do we create a PR and move it to QA to merge without resolving the thumbnail overlapping content UI issue?

[djbrooke]

@mheppler @pdurbin thanks for the discussion and for tagging me. Sounds like it's better if this is included in the buttons branch instead of as an independent PR.