Update to new method names in gtsam SfmTrack and SfmData

[akshay-krishnan]

This only changes some method names, for ex: number_measurements() - > numberMeasurements(), add_measurement() -> addMeasurement(), due to the change on gtsam.

GTSAM PR: borglab/gtsam#1082

[akshay-krishnan]

Need to update the GTSAM wheel in the CI, left a TODO in setup.py

[johnwlambert]

thanks for the PR, @akshay-krishnan. A few more names for us to update, according to the CI:

==================================== ERRORS ====================================
______________ ERROR collecting tests/test_two_view_estimator.py _______________
tests/test_two_view_estimator.py:[17](https://github.com/borglab/gtsfm/runs/5113140405?check_suite_focus=true#step:7:17): in <module>
    EXAMPLE_DATA = io_utils.read_bal(gtsam.findExampleDataFile(GTSAM_EXAMPLE_FILE))
gtsfm/utils/io.py:137: in read_bal
    num_images = sfm_data.number_cameras()
E   AttributeError: 'gtsam.gtsam.SfmData' object has no attribute 'number_cameras'
___________ ERROR collecting tests/bundle/test_bundle_adjustment.py ____________
tests/bundle/test_bundle_adjustment.py:15: in <module>
    EXAMPLE_DATA = io_utils.read_bal(gtsam.findExampleDataFile(GTSAM_EXAMPLE_FILE))
gtsfm/utils/io.py:137: in read_bal
    num_images = sfm_data.number_cameras()
E   AttributeError: 'gtsam.gtsam.SfmData' object has no attribute 'number_cameras'
_______________ ERROR collecting tests/common/test_gtsfm_data.py _______________
tests/common/test_gtsfm_data.py:[19](https://github.com/borglab/gtsfm/runs/5113140405?check_suite_focus=true#step:7:19): in <module>
    EXAMPLE_DATA = io_utils.read_bal(gtsam.findExampleDataFile(GTSAM_EXAMPLE_FILE))
gtsfm/utils/io.py:1[37](https://github.com/borglab/gtsfm/runs/5113140405?check_suite_focus=true#step:7:37): in read_bal
    num_images = sfm_data.number_cameras()
E   AttributeError: 'gtsam.gtsam.SfmData' object has no attribute 'number_cameras'
______________ ERROR collecting tests/utils/test_serialization.py ______________
tests/utils/test_serialization.py:15: in <module>
    EXAMPLE_DATA = io_utils.read_bal(gtsam.findExampleDataFile(GTSAM_EXAMPLE_FILE))
gtsfm/utils/io.py:137: in read_bal
    num_images = sfm_data.number_cameras()
E   AttributeError: 'gtsam.gtsam.SfmData' object has no attribute 'number_cameras'
=============================== warnings summary ===============================

[ayushbaid]

You might also need to update the wheel links in the README.

[ayushbaid]

nit: you can export the name to make it easier from next time.

[akshay-krishnan]

udpated, hopefully the change is what you meant.

[johnwlambert]

looks better!

[johnwlambert]

LGTM, very nice. Thanks Akshay