Use e2image to move/copy ext[234] file systems (#721516)

Use e2image features added in e2fsprogs 1.42.9 to move/copy
an ext[234] file system more efficiently by skipping unused blocks.
Fall back to the internal copy algorithm if e2image is not found
or does not support move/copy.

Bug #721516 - Use e2image to move/copy ext[234] filesystems
Avoid using String::ucompose to build command lines

The String::ucompose method is for easy, i18n-friendly composition of
strings with Gtkmm.  From past experience, String::ucompose should not
be used to build command lines due to differences in how locales handle
number translation.  More specifically, not all locales use number
separators (spaces, commas or periods) and the decimal separator
(period or comma) in the same way.

The problem with using String::ucompose for command lines was
originally encountered and corrected in the following commit:

Fix attempt data rescue fail to open read-only view (#673246)
e494eca1f7798d98cc4e83fb2875f1c409d0ac98