Recurring Transaction Check Fix

[rguida]

This is a fix (plus a small improvement) of the Recurring Transaction Check.
Currently, the check is performed for all recurring transactions, regardless of whether they will be applied.
This results in an incorrect calculation in case the sum of all the transactions, even the ones that would not be immediately applied, would bring the balance below the minimum balance.

In short:

• The check is now performed just before the transaction is applied.
• The message box shows some details to help the user decide

Please do not forget to update the mmex.pot file and write information about the fixed bug in the prerelease page.

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This change is 

[whalley]

Looks good, but the strings need to be enclosed in _( ) to signify that language translation applies.

[rguida]

Looks good, but the strings need to be enclosed in _( ) to signify that language translation applies.

Done.
I changed my approach to minimise the number of strings to be translated.