Make sys.path entry independent of location

This makes it possible to invoke "mp" through a symbolic
link from anywhere.

We use as a reference the location of the actual scripts/mailpile
script, with all symlinks resolved, rather than the name the user
used to invoke the script, which may e.g. be a symbolic link in ~/bin/.

As a bonus (?), the script can now be invoked directly as
scripts/mailpile, rather than through the 'mp' symlink.
Added note about installing lxml

Installing the lxml package requires certain header files to be found on
the system. For Debian-based systems with apt-get, I added a small note
from Stack Overflow on what packages to install to get those header
files.
you can now "minify" javscript files with make js
Merge pull request #255 from changlinli/master

Added note in README about installing lxml
Merge pull request #254 from gnprice/master

Make sys.path entry independent of location
README updates
Updated Gravatar call to use HTTPS
Added friendly_datetime to jinja extensions
Refacoted message view a bit
Worked on Message view a bit more
i18n support
Updated Makefile to support PO/POT file generation.
i18nized hardcoded English strings for multilanguage support.
Note: Some strings were not added, as they were obviously temporary.
Mailpile i18n strings.
i18n: A few fixes to defaults
i18n: generation scripts
Fixed escaping bug.
i18n: Updated charset on english .po
Shipping mo files.
'->"