Polyclonal

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- Add ``addtl_slider_stats_as_max`` to ``lineplot_and_heatmap``.
- Show *escape_std* in ``PolyclonalCollection.mut_escape_plot`` and ``PolyclonalCollectios.mut_icXX_plot``

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- Add ``heatmap_lims_from_slider_init`` option to ``lineplot_and_heatmap`` so that by default heatmap range is set by data shown with initial slider stats. Set this option to ``False`` if you want old behavior for plot limits
- Set default ``init_floor_at_zero`` for ``mut_icXX_plot`` to be ``True`` like for other plots.
- Ensure that wildtype identity is always shown in heatmap tooltips even if mutation is filtered.

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- Change ``lineplot_and_heatmap`` parameter ``addtl_slider_stats_hide_not_filter`` (which is used to make the escape heatmaps) so that mutations that have null escape but a non-null but hidden value are shown as grayed out (hidden) rather than missing. The use case is so that deleterious mutations that don't have escape measured but fail the functional effects filter are shown grayed out to indicate that they were measured and are deleterious, rather than leaving them out which implies they were not measured.
- Fix bug where ``scale_stat_col`` to per-model values in tooltips when using ``PolyclonalCollection.mut_escape_plot`` and ``PolyclonalCollections.mut_escape_icXX``.
- Add ``min_times_seen`` filter to ``PolyclonalCollection.mut_escape_corr`` and ``PolyclonalCollection.mut_escape_corr_heatmap``.

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- Fix bug in ``Polyclonal.icXX`` when the ICXX is at the bounds.
- Increase the range of ``min_c``, ``max_c``, and ``check_wt_icXX`` in ``mut_icXX``-related methods.

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- Fixed bug introduced in version 6.3 in ``PolyclonalCollection.sites`` when ``sites`` are integer.

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- Ensure ``PolyclonalCollection.sites`` attribute is always defined.
- Move testing from Travis to GitHub actions.