[BZ#671607] Support command line text filters

Submitted by Adam Russell

Link to original bug (#671607)

Description

I often times find myself wishing meld supported more command line options similar to diff, especially regarding ignoring whitespace. It is inconvenient to have to start meld, manually check/uncheck the text filters I want in the preferences, and then restart meld with the actual diff I desire. Instead, I'd rather just be able to pass in options to meld in a similar fashion to diff, e.g.:

   -i, --ignore-case
          ignore case differences in file contents

   -E, --ignore-tab-expansion
          ignore changes due to tab expansion

   -b, --ignore-space-change
          ignore changes in the amount of white space

   -w, --ignore-all-space
          ignore all white space

   -B, --ignore-blank-lines
          ignore changes whose lines are all blank

   -I, --ignore-matching-lines=RE
          ignore changes whose lines all match RE