Temp files cleanup
Currently, the process of exporting into different formats produces temporary files. These files are stored under temp folders where the naming convention for their creation is based on a generated random hash.
We should change that convention and instead of that we should provide some meaning to the naming convention which will help on the cleanup.
The temp folders should be named based on the timestamp of their creation. By doing so we will have the ability to create cron jobs that can delete older temp folders based on a configurable interval. The existing cleanup mechanism is not sufficient or even not existent in some cases.
The above should be applied for the case of folders and actual files. This applies for the cases of exporting to EPUB, ICML, and PDF.