Changes to handbook. Changed exposure calculator dialog to remove "Sub-" from title, (and other minor issues)

exposurecalculatordialog.ui: Changed dialog to remove "Sub-" from title, since the calculator includes calculations for integration. exposurecalculatordialog.cpp: Raised the limit for noise increase even higher, (after discoveriung that some photographers use lucky imaging even at dark sky sites) capture.ui: changed tooltip for Exposure Calculator button. ekos-capture.docbook: updated png image of exposure calculator so that title bar reflects the changes above. Corrected link to Wikipedia Sky Brightness. Corrected a few grammatical issues.