Add support for msgmerge --no-fuzzy-matching

msgmerge creates fuzzy entries by default when it sees similar entries
in the "old" version of the file. This is helpful when there's only a
small modification to a string, but on the other hand, it can cause
problems with less experienced translators who accept fuzzy entries
without really checking.

Use --no-fuzzy-matching flag to disable this (and have better
performance), optionally. Bind the behavior to "Consult TM when updating
from sources". It is similar enough to TM updates to make sense, and it
avoids adding yet another setting (to be revisited if there are
complains about this).
Fix crash when clicking "Don't show again"
Skip OS X sandboxing code when not sandboxed
Detect file wrapping and apply it when saving

Detect line wrapping setting used to create the PO file and preserve it.
This allows handling --no-wrap files nicely, as well as preserving
non-standard column widths. Still use the default for new files.
Only preserve file wrapping if not disabled

Reuse the existing keep_crlf setting and only preserve file's wrapping
if the setting is on (the default). Change its UI label to reflect that
it no longer affects only line ending characters, but also line endings
wrapping.
Detect file's line endings when loading, not saving

Remember line endings of the file as it was loaded and preserve it when
saving (if so configured). Previously, Poedit would look at an existing
file being overwriten when saving and use its line endings. That was
both less efficient and not quite logical.
Make wrapping configurable in preferences

Make it possible to enable/disable wrapping of PO files and set wrap
width in preferences. The default is to use gettext defaults (wrap at
column 79) and to preserve edited file's settings.
Merge branch 'proper-line-wrapping'

Fixes #94.