Fix: various issues

[s520]

This PR contains many changes and improvements.

Import

• Fixed a problem that files that are not UTF-8 or files with tabs cannot be read.
• Fixed a problem that texture files could not be read correctly.
• Preserve csv object's unique attributes in custom properties.

Export

• Fixed an issue where Global scale was not working.
• Output csv object specific attributes from custom properties.

Please release as v0.6.0 after merging.

[maisvendoo]

Very good and greate job! Thank you very much for it! I released of version 0.6.0 with your changes

[s520]

Thank you for merging.
I confirmed that the chardet folder of "blenderCSV-v0.6.0.zip" is empty.
If this happens, an error will occur.
Please replace it with the attached zip file.
blenderCSV-v0.6.0.zip

[maisvendoo]

Ok, file is changed

[s520]

Thanks!