Modularize geojson into utilty

[doneill]

Created a geojson utility for future user, for subject tracks reverted to the API response

Proposed Changes

• Create generic geojson utils source
• Create ExportToFile to create the geojson files
• Removed redundate conversion code

Expectation:

• Exporting subject tracks by id works as expected

# generated tracks for last 3 days
er subjects -s {subject-id} -t -u 3 -e

• All subjects test pass

=== RUN   TestSubjects
=== RUN   TestSubjects/successful_response
=== RUN   TestSubjects/server_error
=== RUN   TestSubjects/empty_response
--- PASS: TestSubjects (0.00s)
    --- PASS: TestSubjects/successful_response (0.00s)
    --- PASS: TestSubjects/server_error (0.00s)
    --- PASS: TestSubjects/empty_response (0.00s)
=== RUN   TestSubjectTracks
=== RUN   TestSubjectTracks/successful_response
=== RUN   TestSubjectTracks/subject_not_found
=== RUN   TestSubjectTracks/empty_subject_ID
--- PASS: TestSubjectTracks (0.00s)
    --- PASS: TestSubjectTracks/successful_response (0.00s)
    --- PASS: TestSubjectTracks/subject_not_found (0.00s)
    --- PASS: TestSubjectTracks/empty_subject_ID (0.00s)