Update names of neurodata_types, assigned names, and corresponding code

[oruebel]

Fix #32
Fix #27

This PR:

• Rename sweeps to simultaneous_recordings
• Rename Sweeps to SimultaneousRecordingsTable
• Rename sweep_sequence to sequential_recordings
• Rename SweepSequence to SequentialRecordingsTable
• Rename runs to repetitions
• Rename Runs to RepetitionsTable
• Rename conditions to experimental_conditions
• Rename Conditions to ExperimentalConditionsTable

For this refactoring this PR updates:

• The type definitions and assigned names in the specification
• The icephys container classes and associated functions to follow the new naming conventions
• The icephys tests to work with the new function/parameter/argument names
• The example notebooks to work with the new function/parameter/argument names
• The example in the README to work with the new function/parameter/argument names