Migrate preferences to andlogview-named directories

[mlopatkin]

This is something that I forgot to do before 1.0 😿

There are several places where an old name is still used:

1. Configuration directories (~/.logview/, %APPDATA%\logview\)
2. SDK download location (~/.logview/, %LOCALAPPDATA%\logview\)
3. Preference file names (logview.properties, logview.json)
4. Log file (/tmp/logview.log, %TEMP%\logview.log)

Ideally, these should be named AndLogView where applicable. Additionally:

• On Linux, we should follow the XDG directory specifications.
• On macOS, log files should be stored in some user-accessible place. AFAIR, it isn't /tmp there, but some place in /var.
• .properties support should go away

To preserve user data, a migrator should be implemented. Migration can also be backported to 1.0.X, if necessary.