[TW-81] Compressed option for reports

_Aikido Guy on 2012-01-05T04:52:07Z says:_

I'd like reports to be a little smarter:
1) Completely remove a column if no entries are in the column, and
2) Completely remove a column if all entries are the same.

For example, in 1.9.4 I have a custom report that gives the following output:
```
A ID R Deps Tags Due Countdown Project Description
80 one 11/12/23 12 days P1 desc 1
2011/12/23_04:08 comment 1
91 yearly one 12/1/1 3 days P2 desc 2
101 3months one 12/1/4 23 hrs P2 desc 3
98 3months one 12/1/4 23 hrs P2 desc 4
79 one 12/1/4 14 hrs P1.A desc 5
94 one 12/1/6 -1 day P2 desc 6
96 2weeks one 12/1/17 -12 days P2 desc 7
102 3months one 12/4/3 -2 mths P2 desc 8
82 one 12/6/1 -4 mths P1 desc 9
84 one P2 desc 10
```

But it could be nice to have a 'compress' option so that if I have it turned on, I could then obtain the following report instead:
```
ID R Due Countdown Project Description
80 11/12/23 12 days P1 desc 1
2011/12/23_04:08 comment 1
91 yearly 12/1/1 3 days P2 desc 2
101 3months 12/1/4 23 hrs P2 desc 3
98 3months 12/1/4 23 hrs P2 desc 4
79 12/1/4 14 hrs P1.A desc 5
94 12/1/6 -1 day P2 desc 6
96 2weeks 12/1/17 -12 days P2 desc 7
102 3months 12/4/3 -2 mths P2 desc 8
82 12/6/1 -4 mths P1 desc 9
84 P2 desc 10
```