Fix illegal RosBag keys by replacing spaces with underscores

[gravityrail]

Re-posting of #1129

This change also updates the format version from 3 to 4

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When attempting to read the file with ROS Kinetic, I get the following error:

running rosbag...
[ INFO] [1517843870.611453253]: Opening /data/depthstream.bag

[FATAL] [1517843870.640881632]: Character [ ] at element [32] is not valid in Graph Resource Name [/device_0/sensor_0/option/Visual Preset/value].  Valid characters are a-z, A-Z, 0-9, / and _.

It appears that recent versions of ROS reject the option keys generated by librealsense.

This patch fixes this by replacing spaces with underscores late in the processing, so that Visual Preset becomes Visual_Preset.

[gravityrail]

Re-reading the specs from this comment, I am not sure I've done this right. I am new to this code (and haven't written C++ for about 20 years) so it would be helpful if someone with more familiarity with both could have a shot at this.

[EverettBerry]

Would be great to see this merged. Just ran into it with a fresh ROS install.

[radfordi]

Fixed by #4537.

[dorodnic]

Better late then never :) @gravityrail thank you for the original suggestion and the pull-request.