Use new discretisedfield syntax

[samjrholt]

Sam:

• dw-pair #17
• dynamics #18
• energy #19
• first-ubermag #20
• mag2exp #21
• magnetisation0field #22
• python-basics #23
• 07 #24
• 08 #25
• 09 #26
• 10 #27
• 11 #28
• 12 #29
• 13 #30
• choosing runner #31
• energy term computations #32

Swapneel:

• field opperation 2
• Update finite temperature notebook #48
• Update fixed subregions notebook #49
• Update hysteresis notebook #50
• Update multiple energy terms notebook #51
• Review negative exchange between layers notebook #52
• Review periodic boundary conditions notebook #53
• Update RKKY notebook #54
• Update sine-hysteresis notebook #55
• Update space and time varying field notebook #56
• Update spatially varying parameters notebook 1 #57
• Update spatially varying parameters notebook 2 #58
• Update STT domain wall motion notebook #59
• Update time dependent field and current notebook #60
• Update time dependent field notebook #61