Better output for double variables / Allow custom format

While a float variable is shown as 1.23456E+010 in the "Locals & Expessions" windows, a double variable with the same value is shown as 12345600000.

Expected:

• large double values should be shown in exponential format too

Bonus:

• provide the possibility to format a float/double value according the users needs
  • number of digits shown
  • format 'f' or 'e'
  • Bonus++ for a format relating to SI exponential units (i.e. the best fitting format ..., 10E-6, 10E-3, 10E0, 10E3, 10E6, 10E9, ...)