templates: Fixed timeago_script() usage

This broke when the scripts were moved to the end of the
HTML files... sorry!
templates/tracking/list: Fixed external tracking button

tracking_type == 0 wasn't captured by the condition...
change imprint to Turbo
tracking: Removed external aircraft tracking feature again

The only current data source agreed on not continuing this service due
to legal and moral privacy issues.
imprint: Load imprint contents from the INI file directly
lib/analysis: Extracted from_seconds_of_day() function
i18n/de: Fixed typos
lib/string: Fixed re.sub() usage

The parameters were switched, which led to wrong results...
lib/string: Fixed non_alpha_re regexp
tests: Added unittest for skylines.lib.string
SQL: Reset empty logger IDs

The broken lib.string caused empty logger IDs, which have to be set to
NULL instead so that the igc_headers URL can be called to reanalyze them.
.ini: Changed sqlalchemy.url prefix to postgresql://

postgres:// is deprecated
tests/lib: Added unittest for skylines.lib.base36
lib/base36: Simplified method names
lib/formatter/flight: Moved code into Jinja2 template for better i18n
templates/tracking: Removed unused/empty block
templates: Added user_link/club_link macros
templates/macros: Added airport_link macro
i18n: Updated .pot file
lib/igc: Parse HFDTE line from IGC files