Allow user to re-enable auto-scaling of colour-bar in Instrument view

[Anders-Markvardsen]

This issue was originally TRAC 2693

Above and below the colour-bar in the Instrument view
there are two input boxes where the user can manually
set the colour-scale. Once set the colour-scale will no
longer auto-rescale. Allow user to force auto-rescaling
by leaving one of the two boxes empty.

[Anders-Markvardsen]

@NickDraper (2011-04-27T07:36:04):
Bulk move of tickets at the end of iteration 28

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@NickDraper (2011-06-27T08:20:28):
"New" tickets moved at the code freeze of iteration 29

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@NickDraper (2011-09-19T09:30:58):
Bulk move of tickets to iteration 31 at the iteration 30 code freeze

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@NickDraper (2012-01-09T09:43:37):
Moved to iteration 33 at iteration 32 code freeze

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@NickDraper (2012-04-30T14:14:41):
Moved at end of release 2.1

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@NickDraper (2012-08-10T12:45:04):
http://www.mantidproject.org/Release_Notes_2_2_Full_List

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@NickDraper (2012-10-28T11:39:19):
Moved to milestone 2.4

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@NickDraper (2013-01-28T09:23:25):
Moved at the code freeze for release 2.4

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@NickDraper (2013-04-29T09:50:02):
Moved to r2.6 at the end of r2.5

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@NickDraper (2013-07-26T13:55:02):
Moved to backlog at the code freeze for R2.6

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@NickDraper (2014-02-14T11:07:56):
bulk move to assigned at the into of the triage step