Add support for new-style tensorboard images

[coveralls]

Pull Request Test Coverage Report for Build ced3e857-8bf1-4488-b511-39ca4c3b7cd9

• 28 of 43 (65.12%) changed or added relevant lines in 4 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 59.344%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
wandb/internal/run.py	11	13	84.62%
wandb/internal/tb_watcher.py	4	8	50.0%
wandb/integration/tensorboard/log.py	12	21	57.14%
<!--	Total:	28	43	65.12%	-->

Files with Coverage Reduction	New Missed Lines	%
wandb/internal/tb_watcher.py	2	26.63%
<!--	Total:	2		-->

Totals
Change from base Build 4c0fef06-246f-487f-89be-9c84a2cdb154:	0.02%
Covered Lines:	11524
Relevant Lines:	19419

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💛 - Coveralls