[test.main] added debug logging switch
[common.configuration] added ctor taking a sub_id

This can be used to put a given config instance into a subtree on the fly,
e.g. one can now do
```
std::cout << Configuration(config, "sub") << std::endl;
```
instead of
```
Configuration tmp;
tmp.add(config, "sub");
std::cout << tmp << std::endl;
```
[common.logging] removed obsolete header, whitespace

I left the {f,o,s}stream includes in place although they are not needed
as far as I can tell. Remove them too, @renemilk?
[common.logging] added DSC_LOG_DEVNULL
[common.color] added bold_white()
[common.logging] added elapsed_time()
[common.logging] added first draft of timed and colored console output

This can be used like:
```
DSC_LOG_INFO_TIMED("main") << "doing stuff..." << std::endl;
```
[la.container.interfaces] added first draft of sup_norm() to matrices