Make folder to store titles and scripts configurable in Kdenlive Settings

Don't create the kdenlive-renderqueue folder if not necessary, and delete it if no script is stored.
Fixes #812
1 job for master in 60 minutes and 23 seconds (queued for 48 minutes)
Status Job ID Name Coverage
failed #73080
linux kf5-qt5 qt5.12


Name Stage Failure
linux kf5-qt5 qt5.12 Build The script exceeded the maximum execution time set for the job
tests/trimmingtest.cpp                       863     863   100%   
thumbnailer/mltpreview.cpp 70 0 0% 31,33,37,41-42,45,47,50,52-53,55-58,60-65,67-71,75-79,82-84,87,89-91,94-97,100,102-105,108-109,112,114-115,117-122,124-126,128-130,132,134-136,138,141,143
TOTAL 76354 14747 19%
Uploading artifacts for successful job
Uploading artifacts...
build: found 1984 matching files and directories

ERROR: Job failed: execution took longer than 1h0m0s seconds