Hijacked ImplNumericGetValue() to parse fractional strings. It now searches for
'/' and build 3 string segments for mixed fractions: whole number, numerator
and denominator. It then follows the previous conversions and checks for
decimal formats. The output string remains as a decimal formatted string for
simplicity and standardization.

Change-Id: Iad842e0ef2b1f637025b09401b10fe93f90e0fba
Reviewed-on: https://gerrit.libreoffice.org/13225Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>