## Summary
Currently `OurSortFilterProxyModel` class is implemented in the same file with `ConversationListModel` class, which would likely grow in the future.
This MR separates `OurSortFilterProxyModel` class into its own separate file renaming it to `ConversationsSortFilterProxyModel`
https://invent.kde.org/kde/kdeconnect-kde/-/merge_requests/229
## Summary
This adds character counter below the “Send” button in SMS conversation. It
uses format XXX/Y where XXX is number of characters that can be added
without splitting the SMS into multiple messages (see article
Concatenated SMS on Wikipedia). Y is number of messages in in current
concatenated SMS. The counter is not visible when insertion of 10 7-bit
or 16-bit (depends on SMS encoding) does not create concatenated SMS.
SMS encoding is automatically guessed. 8-bit encodings are not
supported. If the message contains characters that are not supported by GSM 7-bit
encoding, counter automatically switches to UCS-2.
## Test Plan
Try entering some text that is longer than 150 characters in [GSM 03.38 encoding][1] or 60 characters in UCS-2. Number of remaining characters should be visible below the “Send” button. The character counter should show `0` at exactly 160 or 70 characters. Inserting one character should switch the counter to [Concatenated SMS][2] mode when number of messages is shown.
It should show exactly same number as SMS app in Android.
## Screenshots
These images are in APNG.
[1]: https://en.wikipedia.org/w/index.php?oldid=932080074#GSM_7-bit_default_alphabet_and_extension_table_of_3GPP_TS_23.038_/_GSM_03.38
[2]: https://en.wikipedia.org/w/index.php?oldid=943185255#Message_size
## Summary
Start a conversation with contacts having no previous conversation with.
It is currently only possible to use the messaging app to send a message to a conversation which already exists.
This patch implements this feature by integrating all contacts having no prior conversation with the recent conversations in the recent conversation list and at the bottom in a sorted manner, something like this,
The contacts are stored in the recent conversation list model as a conversation but with INVALID conversation ID and INVALID conversation DATE.
## Testing
Testing just needs kdeconnect daemon to be recompiled and executed.
