Dimcli

* Added DSL grammar for DSL V2.8
* New utility function: [utils.explode_nested_repeated_field](https://digital-science.github.io/dimcli/modules.html#dimcli.utils.misc_utils.explode_nested_repeated_field)

* Warning messages included with `query_iterative` outputs.

* Added DSL grammar for DSL V2.7

* Minor code cleanups

* Added DSL grammar for DSL V2.6

* New parameters for [DslDataset.as_dataframe()](https://digital-science.github.io/dimcli/modules.html#dimcli.core.api.DslDataset.as_dataframe)
* Improvements to the `--nice` and `--links` rendering of dataframes with Dimesions data
- with hyperlinks, drop IDs if title is present
- affiliations as a list with GRID links
- generic 'default_transform' method for extra column not in transformations
* Test suite for magic commands
* New feature: `verify_ssl` option for `login()` method