Add 'graft' command

[drroe]

Adds a new command, 'graft' which can be used to graft all or part of one COORDS set onto another COORDS set.

> help graft
  [help graft]
	src <source COORDS> [srcframe <#>] [srcfitmask <mask>] [srcmask <mask>]
	tgt <target COORDS> [tgtframe <#>] [tgtfitmask <mask>] [tgtmask <mask>]
	name <output COORDS> [bond <tgt>,<src> ...]

Also adds manual entry and a test.

Note, this functionality was already possible with existing commands (see the test in Test_CombineCrd); this command just simplifies the process a bit.

[lgtm-com]

This pull request introduces 1 alert when merging f414ea1 into 53250cf - view on LGTM.com

new alerts:

• 1 for Constant return type