Issues related to the search&replace functionality

Issues related to the search&replace functionality:

• BUG The replace command doesn't work for Text - fixed in 0120a671
• Add an option to search only in the "Current selection only"
• Searching in a spreadsheet should match only to the precision of the columns's print format #37 (closed),
• Add the new search&replace entries to the menu for column headers and the context menu in project explorer
• Add the option to use regular expressions also for Numeric values,
• Rename "DateTime" to "Date&Time" - fixed in 0120a671
• Add an option to apply the replace pattern in all spreadsheets