Special characters in note/folder names break the application

[rimesc]

Including a / character in a note/folder name results in spurious errors (under MacOS):

• For folders: Workspace not found
• For notes: ENOENT: no such file or directory

[rimesc]

In both cases, it's because the / character is interpreted as a directory separator. Because of this, in the first case, we fail to find the parent directory of the new directory. The second case is more confusing, because I'd expect to get a Folder '...' not found error, for similar reasons.

There are probably other reserved characters that break the application. We should either ban them or find a way to sanitise the file name (which would probably mean having to store the user-visible name separately).

[rimesc]

Note, on MacOS at least, it is possible to have file names that appear to contain / characters in UI applications, although in the underlying file system / is replaced with :. You can't, on the other hand, have : in the name displayed in the UI.