Bug Fixes and a new Hexsticker

• fixed bug in linear model equation where slope and intercept values were switched
• fixed bug where flip barplot was not working (auto flipped barplot already supported)
• added group aesthetic and other enhancements for pairs plot
• bug fixes for expansion, zooming with user input (plots with only x variable(s) or only y variable(s))
• restored target window annotations to work with factor/character x axis
• added the possibility to change the size and linetype of density plots
• added the possibility to choose the shape of boxplot outlier points
• added options for x and y scale tick formatting are now visible when pairs plot are active
• added options for identity line and for placement of custom/target text at plot edges
• added checkbox to recode numeric variables with -99 to missing
• removed ggstance dependency by adding needed positions to global.r
• fixed typos in Visualizing Summary Data vignette data labels