Base alternative can be purged

[soininen]

Currently, we protect the 'Base' alternative: it cannot be removed from the database. However, when purging alternatives, also alternative id 1 (i.e. 'Base') gets purged.

This is a non-issue if we lift the protection as suggested in spine-tools/Spine-Toolbox#2331

[jkiviluo]

We shouldn't enforce a particular base alternative name. It's hard coding. For example, sometimes user may have two equal bases 'north' and 'south'. One adds a north part of the model and the other south part, but there is no common base. And I don't necessarily want to call my base 'Base', I might want to call it e.g. 'init'.

[soininen]

In case of removal, we actually protect the alternative id, not its name so we aren't hard-coding anything except the existence of at least one alternative. Anyway, this issue is not about whether we should have that guarantee. Rather, it is about a bug if we choose to keep the guarantee.

[jkiviluo]

I think this is to be discussed in the next Toolbox telco.

[soininen]

It was decided in the 2024-04-09 developer meeting that we will allow deletion of the 'Base' alternative.