Forcing all extensions to report as lower-case
Fixed issue with broken UTF8 folder/file names

Improper response reading could produce non-UTF8 paths to files and
folders causing all types of unexpected errors (can't stat path, reporting
it as no-rights, can't preview file content).

Observed on wrong UI behaviors for folders with ąćęłńóżź...
Made again 4MB files are acceptable for preview
Moved 'Target Navigator' menu above 'Help'