Normalize 12*2^x*3^y to 2^(2+x)*3^(1+y)

[Axel Kramer]

Normalize Times() expressions with leading integer factors and integer powers as factors if possible.

Examples:

12*2^x*3^y ==> 2^(2+x)*3^(1+y)

8*2^x ==> 2^(3+x)

12*2^x ==> 3*2^(2+x)

[Axel Kramer]

See commit 83cafa1