model/event: Skip creating club join events with empty club

Fixes #131
Merge pull request #132 from Turbo87/empty-club-event-fix

model/event: Skip creating club join events with empty club
model: Encode with `unicode_escape` encoding in __repr__() methods
Merge pull request #133 from Turbo87/repr-encoding

model: Encode with `unicode_escape` encoding in __repr__() methods
scripts: Added basic live tracking analysis script

Only counting the number of live tracking fixes for now
scripts: Added get_base_query() to tracking/stats.py
scripts: Show tracking sessions in tracking/stats.py
scripts: Added JSON output to tracking/stats.py
scripts: Count session fixes and print duration in tracking/stats.py
scripts: Added quality and dt output to tracking/stats.py
scripts: Fixed tracking/stats.py for empty lists
scripts: Added print_session() to tracking/stats.py
Merge pull request #135 from Turbo87/tracking-stats

Tracking stats
analysis: Reduced the parsing error log level to "warning"

"error" is sending email messages now!
forms/club: Added Uniqueness validator to EditForm name field
validators: Add "That value exists already" to i18n
Merge pull request #136 from Turbo87/log-level

analysis: Reduced the parsing error log level to "warning"
Merge pull request #138 from Turbo87/issue-134

check for unique club names
upload: Prevent IntegrityError on duplicate files in ZIP archives

Fixes issue #137
upload: Check Flight.get() result properly before using it