Improve error message for builder.fill() when starting sites are not in the template builder

Closes #224 (closed)

changed the description

added 4 commits

• 4732c59d - 1 commit from branch kwant:stable
• 80cece92 - builder.fill: add tests for empty template and starting site outside
• 16b56d72 - builder.fill: correctly re-raise error using 'raise ... from ...'
• 40caff74 - builder.fill: raise error when starting with a site not in template

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added 3 commits

• c4ec9c69 - builder.fill: add tests for empty template and starting site outside
• da03d359 - builder.fill: correctly re-raise error using 'raise ... from ...'
• 8c4ac8b6 - builder.fill: raise warning when starting with a site not in template

Compare with previous version

added 3 commits

• 3a02cc2f - builder.fill: add tests for empty template and starting site outside
• 036056ae - builder.fill: correctly re-raise error using 'raise ... from ...'
• d47fd098 - builder.fill: raise warning when starting with a site not in template

Compare with previous version

enabled an automatic merge when the pipeline for d47fd098 succeeds

merged

mentioned in commit 84d1e87f