Fixes for search&replace:

Description

[spreadsheet] fixes for search&replace:

• use "Date & Time" string instead of "DateTime"
• when replacing in text columns, use the replace string from the comobox box for text columns and not for numeric columns
• when replacing via "replace next", make sure also the value in the currently selected cell is replaced before proceeding to next cells.

This addresses bugs reported in #573

Conformity

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

When external dependencies are removed

• Reporting to ...