Add vacuum

[awalter-bnl]

This PR adds the discussed change to how vacuum components are included (see code snippet below for the new structure). It also makes a few back-end changes to how 'print' and 'tab-to-complete' code works but these do not affect the User Interface.

@Jiemin-Li please take a look when you get a chance. @tfg4280 you may also want to take a look as you start to get your head around this work (suggestions/ comments are welcome).

In [3]: print(m1)

m1 ('device')
  "positions":    locations 
  "motors":    Ry_coarse     Ry_fine     Rz     x     y 
  "devices":    
    vacuum 
      "sections":    
        AriSxnC 
          "detectors":    ccg     tcg     ip 
          "positions":    gv     
    slits 
      "positions":    locations 
      "motors":    top     bottom     inboard     outboard 
      "detectors":    currents     
    diag 
      "positions":    locations 
      "motors":    blade     filter 
      "detectors":    camera     currents 

[Jiemin-Li]

The current structure for m1 section is clear to me, especially when printing it in Bluesky,.