added channel names to Observation label

[pmelchior]

simple fix to add the names of the channels to the title of the "Observation" panel it the plotting routines. Makes it easier in multi-obs cases to know what we're looking at.

Also, minor changes in other plot labels. All cosmetic.

[github-actions]

Before [b6c2c73]	After [41bfffc]	Ratio	Benchmark (Parameter)
0	0	n/a	bbox_benchmarks.BoxSuite.mem_bbox_contains(16)
0	0	n/a	bbox_benchmarks.BoxSuite.mem_bbox_contains(2)
0	0	n/a	bbox_benchmarks.BoxSuite.mem_bbox_contains(2048)
0	0	n/a	bbox_benchmarks.BoxSuite.mem_bbox_contains(256)
0	0	n/a	bbox_benchmarks.mem_bbox_creation
56.4±0.6μs	56.2±0.06μs	1.00	bbox_benchmarks.BoxSuite.time_bbox_contains(2)
59.6±1μs	59.5±0.6μs	1.00	bbox_benchmarks.BoxSuite.time_bbox_contains(2048)
59.1±0.1μs	58.7±1μs	0.99	bbox_benchmarks.BoxSuite.time_bbox_contains(16)
58.4±0.5μs	58.0±0.1μs	0.99	bbox_benchmarks.BoxSuite.time_bbox_contains(256)
19.9±0.1μs	19.5±0.04μs	0.98	bbox_benchmarks.time_bbox_creation

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