pango_plot: Fix plot key formatting issues
pango_plot: Fix plot key formatting issues

1) Use font height instead of text height for vertical spacing
2) Fix right alignment problem of key due to bug in PlotTitleFromExpr() where EOF symbol was getting added to string.

stevenlovegrove/Pangolin,mp3guy/Pangolin,stevenlovegrove/Pangolin,mp3guy/Pangolin,mp3guy/Pangolin,stevenlovegrove/Pangolin