* re-introduced linear tonemapping
** uses two parameters - value and exponent. the image will be scaled by value*10^exponent

* changed upper limit of Reinhard pre scale to 20

* added histogram display. doesn't seem to work for linear tonemapping for some reason.

* added two noise reduction filters, median and chiu. No parameters for these yet - but the median is 3x3 in size, and chiu is 3x3 (including centre).

* added processing progress feedback to the status bar.

* added a few extra checks to prevent a new processing thread starting before the running one has finished.

* managed to double the .exe size  = 4mb :(