[log] simplify loading details around selected commit

No need to implement some AroundProvider: we can take data right from
the table model, by row index.

DataGetter#getCommitData has to be Nullable now, because there can be
"empty" rows holding no commits.

VcsLogFilterer can't use new getCommitData, because there is no table
model to supply: it actually gets created from the filterer. However,
we expect details to be in the cache, so there is no need to load
around anyway.
[git] write less garbage to the log
[git] remove unused
[git] DRY

'git log --no-walk <hashes>' behaves the same as 'git show <hashes>'
because --no-walk tells git "Only show the given commits,
but do not traverse their ancestors".

'unsorted' tells Git to return commit details in the same order as
hashes passed to the command.
Among current usages of the method, we don't care about the order,
but seems correct for possible future methods relying on this.
bundle junit 4.11
Merge remote-tracking branch 'origin/master'