[dialogs] update dialog lines/headings in Process() rather than by sending messages around
[dialogs] support use of textbox (id 9) for lines instead of 3 labels
[confluence] OK dialog can use a textbox
[dialogs] use vector<string> for lines rather than a constrained value now that we can take a textbox
[dialogs] adds SetText() for setting all lines in a dialog at once
[dialogs] add ShowAndGetInput() statics for SetText() in Yes/No and OK dialogs
[dialogs] no need to set default labels for lines and heading
[dialogs] store a single string rather than vector of strings for lines
Merge pull request #3573 from jmarshallnz/dialog_textbox

Support a textbox in dialogs derived from dialogboxbase (ok, yes/no, progress etc.)