Add new panel option for display_total_marked_size() to apply three different styles

[michael-o]

Currently, display_total_marked_size() supports only one style to display the marked size. Some people would prefer to see the raw, scaled or even both values. It should be made configurable through the panel options. Some effort has already been made in #3666.

The modes:

Mode 'raw':

100000 B in 10 files
560000000000 B in 1001 files

Mode 'scaled':
SI (base 10):
100 B in 10 files
100 kB in 100 files
950 MB in 200 files
560 GB in 1001 files
IEC (base 2):
100 B in 10 files
98 KiB in 100 files
940 MiB in 200 files
1020 MiB in 220 files
550 GiB in 1001 files

Mode 'both':
SI (base 10):
100 B in 10 files
100 kB (100000 B) in 100 files
950 MB (950201123 B) in 200 files
560 GB (560100245124 B) in 1001 files
IEC (base 2):
100 B in 10 files
98 KiB (100400 B) in 100 files
940 MiB (985661900 B) in 200 files
1020 MiB (1069547520 B) in 220 files
550 GiB (590558003200 B) in 1001 files

Note that in 'both' mode with a value below 1000 bytes or 1024 bytes, 'raw' mode is applied to avoid duplicate information.

The new panel option: Total marked size style: [raw, scaled, both] (need to investigate how to do this)
Serialized as "total_marked_size_style" with default value of "scaled".