topics: add a new flag --age which will show last touched time for topics This adds a new flag `--age` to `hg topic` command which will show topics sorted by their last touched time and will also show the last touched time for them. This patch also adds a simple test to make sure the flag does not breaks by future changes. Adding more tests showing output like "3 hours ago", "2 minutes ago" etc will change as the code takes time.time() into account which will increase with time, and hence the output will change, so we need some static output like a date.