[Output] Change scatter plot style
[Output] Enable realtime graph
[Output] Enable real time graph
[Output] Fix saving figure
Host collision control and report

Removed collision control by dumping all outgoing packets into link
buffer. Also changed report function to give rates in Mbps instead of
packets/s.

On a minor note, I'm not sure why the flows parameter was changed to
default to None, so I made it default to an empty dictionary again.
Merge remote-tracking branch 'origin/master'

Conflicts:
	host.py
Fixed weird merge conflicts.
Grammar error.
Added window size control for flow.
Added reporting for window size.
Changed send/receive rates to Mbps.
Variable renaming

Renamed data_sent and data_received fields to amt_data_sent and
amt_data_received, respectively, for clarity.
Modified mutators of packets.

Added set_timestamp() method and renamed set_sequence_number() method to
set_seq_num() to match get_seq_num(). Also updated test code.
[TEST0] Fix broken master
- Revert default flow value to None in Host
- Fix Flow's rate conversion factor (integer division error)
- Fix output graph's unit
Merge branch 'master' into Router

Conflicts:
	env.py
Merge branch 'router'
Merge pull request #25 from kexinrong/master

Syncing router branch with master.