[log] Using commit time instead of author time. Step 1. Renaming.

Rename authorTime -> time everywhere in the Vcs Log: this is just
"some time which we consider for the log primary details".
[log] Use commit time instead of author time. Step 2. Renaming.

Rename commitTime -> authorTime everywhere in the Vcs Log.
Actual change in git provider will follow.
[log] Use commit time instead of author time. Step 3. Actual change.

Actually supply commit time instead of author time for GitLogProvider.

This fixes two issues:
1. Slight confusion if user sees an "older" commit above a "younger"
   one (because the older one was re-committed recently by cherry-pick
   or rebase).
2. Major issue in a multi-root project: when commits from different
   repos are joined, they are compared by time. And comparing by
   author time may lead to the situation when a really older
   (possibly much older) commit stays above a younger one,
   which also affects filtering results: a really recent commit may be
   skipped from the recent results (but then may suddenly appear when
   filtering is made via VCS).