refactor devices, utils, ... into subdirectories

[prjemian]

Project is growing and the various files have many definitions each. Divide files (such as devices.py) into directories (such as devices) and make modules as appropriate.

[prjemian]

Changeset 4b8ef0e belongs to this issue, not #288

[prjemian]

Not convinced these changes result in a positive improvement to the package. Beginning to look more like a re-arrangement that needs more work, causes more work, and might not make the package easier to understand and maintain.

Identify the substantive changes in this branch and create issues for each, then resolve each in master branch.

[prjemian]

Create a PR to highlight those changes.

[prjemian]

new issues

• remove unix_cmd #291
• remove list_recent_scans #292
• remove run_blocker_in_plan #293
• plans: lineup needs access to BestEffortCallback instance #294

Here are the changesets involved in the branch:

• commit 4b8ef0e
• commit ffe1f81
• commit 3ef1c40
• commit e51ef5b
• commit 1cc4cd7
• commit a00aa0c
• commit ce9e9a2
• commit 60776bc
• commit 079f544
• commit 59c5b49
• commit 6613e22
• commit dd6c94c
• commit 66223da
• commit 1f30386
• commit ba5d66a

[prjemian]

All changes recovered.