Cross platform config sync

**Is your feature request related to a problem? Please describe.**
I use _CopyQ_ on several desktops - two are _Windows_, and one is _Linux_. I use third party sync tools (currently _Seafile_, previously _Syncthing_) to synchronise the `config` folder of portable installations. This allows me to synchronise both the tab data as well as configuration (I tried the synchronisation plugin, but the installation paths on all my desktops are different, so it does not work; and it does not sync configuration). This setup works well on my two _Windows_ desktops (I have disabled sync of my clipboard tab using sync filters in my sync utility). Unfortunately this is not viable on my _Linux_ desktop because the configuration file name is different (`copyq.ini` on _Windows_ & `copyq.conf` on *Linux*)

**Describe the solution you'd like**
The structure of the configuration directory is similar in both _Windows_ (`C:\PortableApps\CopyQ\config\copyq\`) and Linux (`~/.config/copyq/`). It would be ideal to have identical file names so any changes in configuration as synchronised across all instances.

**Describe alternatives you've considered**
I have tried forcing a sync of the above directories, but with different configuration files, I still have to manually mirror changes.

The only other alternative is to install a separate utility to synchronise both files (`copyq.ini` &` copyq.conf`) to ensure changes are synced, but this is neither efficient nor graceful.

**Additional context**
Although built-in sync of configuration would be ideal, this is not required as part of this feature request. Only making the `config `directory identical is requested, including the configuration file itself.