Provide ability to download example subset of datasets

[heather999]

Addresses a main part of #1 but not entirely in the way that was requested: In the “Browse Dataset” view, is there a way to add a “Select an example subset” button, which when clicked on, will check say 4 tracts that we use in the notebooks On the dev portal, when you visit the Browse Dataset view for any dataset, there is a new button which provides an option to transfer a predefined subset of the dataset being viewed. Clicking the button does not cause the checkboxes to be checked, rather the transfer is initiated. This achieves the desired outcome, but doesn't allow a user to select additional files for download. Is this ok? Well.. I'll put it this way, I don't see a good clean way yet to just check the checkboxes for the subset of files by communicating that information to the template.

[yymao]

Thanks @heather999 -- this looks fine. Although I wonder if people would interpret the "Example Dataset" as not being part of the "real" data set? Should we change the button to "Get an {{exsize}} example subset"?

I also see a way to implement the checkbox --- now that you have defined the filenames in the example subset, we can write a simple javascript to check the boxes with matching filenames. We can implement this latter, of course.

[yymao]

While you are here, I think you can also implement "In the “Browse Dataset” view, list the size in MB or GB" by simply changing Line 64 of web/portal/templates/browse.jinja2

from

<td class="col-md-1 text-right">{{file.size}}</td>

to

<td class="col-md-1 text-right">{{ filesizeformat(file.size) }}</td>

[heather999]

Sure it's easy to change the button. We don't want people to be confused, either by thinking that button is for initiating a transfer of what they select below or thinking that this is some different set of data.

ah I'll grab the bit for the filesizeformat too.

I guess I was worried about adding too much logic to search for those specific entries and slowing down the rendering of the page... but I suppose that is what javascript is for. :)