Ability to set which hours to show in reports

Currently `reports.*.hours = auto` may create reports of different width which is not quite usable for visualisation/readability of timeframes. And `all` is also not good as it shows too many unneeded/unused hours, excluded for example.
So it would be nice to be able to configure which hours should be shown in reports.
For example, I have an exclusions like this:
```
define exclusions:
monday = <10:30 13:30-15:00 >19:00
tuesday = <10:30 13:30-15:00 >19:00
wednesday = <10:30 13:30-15:00 >19:00
thursday = <10:30 13:30-15:00 >19:00
friday = <10:30 13:30-15:00 >19:00
saturday = <10:30 13:30-15:00 >19:00
sunday = <10:30 13:30-15:00 >19:00
```

And I don't want to see hours from 21 till 9 in all reports. So with the option reports will be always of constant width which is good for fast realisation how many time I spend on what. And it also give an ability to increase number of cells for every hour which is also gives better visualisation/readability of reports.