UI/UX Improvements - Custom Database Creation Dialog

[pverscha]

Remarks about the first step of the database creation wizard:

• Select both TrEMBL and SwissProt by default in the dropdown. This is most likely the scenario that most users would like to use.
• Do not use a text field to indicate what the current UniProt-version is. This should be shown as a sentence.

Remarks about the second step of the database creation wizard:

• The filtering of taxa is weird at this moment. If no taxa are selected, no filtering will be applied. But if one or more taxa are selected for filtering, these are the only ones that will be retained in the resulting database. This could be confusing because it seems like the filtering is subtractive (adding taxa will exclude them from the database), but instead it is additive from whenever at least one item is selected. In order to fix this, we could always select the root taxon by default (making it additive filtering in all cases).
• Show 10 taxa by default in the TaxonBrowser (instead of 5).
• Taxa chips are selectable, but should not be selectable.
• We should show how many UniProt-records will approximately be present in the resulting database. (And we need to look into the UniProt API for this).
• The "Search for taxa" explanation should be moved to a separate tooltip (this information is too prominent at this point).
• It's not possible to click on a previous step in the stepper wizard to go back and edit this step. This should be made possible.
• Information that has been selected in the first step of the stepper should be shown as subtext in the stepper header (whenever we go to a next step).

[pverscha]

In order to show how many UniProt-records will be present in the resulting database, we can use this URL-format for the UniProt-API: https://rest.uniprot.org/uniprotkb/search?facets=reviewed&query=taxonomy_id:40674+OR+taxonomy_id:2&size=0

[pverscha]

The amount of UniProt-records associated with a set of selected taxa is now calculated using the UniProt API. Note that the UI for this is not final yet.

[pverscha]

A text field is no longer used for displaying the current version of the UniProtKB database. This has been changed to a regular text element not to confuse our users:

[pverscha]

Also see #244, the UI of the TaxaBrowser has been improved in this PR (making it clearer for users what some of these buttons are meant to do).