Add GPS filtering to task creation flow

[ejcunningham]

Add support to filter images by GPS location during task creation flow

PR fixes #82

Changes

• Add latitude+longitude filters to the task creation form
• Change Image model to default location attributes to invalid values rather than using required=false, which seems to be the same as defaulting to 0 (a valid value) rather than undefined
• Plumb filters through the task POST endpoint and taskQueuer

Note the ticket specifies setting a placeholder text on the form fields, but placeholders appear to be broken on this whole form. Suggest we fix that bug as a separate task.

Test Plan:

• Tested that the UI can correctly reflect filters in image-count
• Verified taskQueuer finds the right files
• Verified image preview shows the right files
• Verified ground truth page and CSV exports still work properly with model changes

[ejcunningham]

Note there are no changes below this point, I just fixed the inconsistent indentation

[naknomum]

generally looks correct to me, except i am not sure if the original issue means the user should be prevented (or warned?) if they enter values outside of the valid ranges. might be a question for @TanyaStere42 to confirm the answer on.

for example, if a user enters a latitude value of 100, should they get a warning/error that they are out of range?

[TanyaStere42]

hiya @naknomum ! Yes, the intention of the ticket is that values outside of the lat/long ranges listed should be disallowed from being entered.

[naknomum]

per updated info (below), i am approving this now.

I talked to the customer and it seems like that validation is important but not blocking. We can go ahead and merge assuming there was nothing else in the code review, and I'll make a new ticket for the form validation (@TanyaStere42)