Addresses issue #bead sparsity/density

Is this a bugfix or an enhancement?
enhancement
Proposed changes:

• add points.multiview.raw_shifts_by_frame to calculate shifts between points on the same frame only
• use raw_shifts_by_frame to generate a shiftmap if the recipe module is configured so

Notes:

• the linking on the same frame only part is sort of important here but a little confusing with declump at the moment, see [thing] deClump/pyDeClump.findClumps - missing doc, questionable gap parameter? #933

Checklist:

• Tested with numpy=1.14
• Tested on python 2.7 and 3.6
• Tested with wx=3.x and wx=4.x [if UI code]
• Does the PR avoid variable renaming in existing code, whitespace changes, and other forms of tidying? [There is a place for code tidying, but it makes reviewing
  much simpler if this is kept separate from functional changes]

If an enhancement (or non-trivial bugfix):

• Has this been discussed in advance (feature request, PR proposal, email, or direct conversation)?
• Does this change how users interact with the software? How will these changes be communicated?
• Does this maintain backwards compatibility with old data?
• Does this change the required dependencies?
• Are there any other side effects of the change?