Toolbar: Reestablish toolbar when other object gets selected

Description

reset lastWorksheet, because if another object gets selected which does not have a worksheet as parent it changes the toolbar as well (like the spreaddsheet). So when the previous worksheet was the same as the newly clicked (and in between for example a spreadsheet). The toolbar gets not rebuild again.

Conformity

• Changelog entry
• Unit tests
• Update INSTALL
• Downport
• Fixes: #785

When external dependencies are removed

• Reporting to ...