Logs.db is always at data_root, even if we set another config directory with -c

fix "Unable to load icon gajim" errors caused by !84

See merge request !87

use 'reverse DNS' convention for desktop and icon files

See merge request !84

HistoryManager was not finding the Logs.db when Gajim was
used with the -c config path argument

fix python errors in client zeroconf

See merge request !82

Disable button if password changing is not supported

See merge request !85

see https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s02.html

Implement chatstate in MUC, as defined in XEP-0085 §5.5

See merge request !11

python-gnupg uses latin1 as default encoding because GPG itself uses
latin1 as default.
We should not override this default with getpreferredencoding, because
getpreferredencoding maybe returns something else than what GPG is configured
on that system.

Example: On Windows
GPG is run in default mode with 'latin1'
getpreferredencoding returns 'cp1252'

The approach would be now to default to latin1 as it is GPGs default.
And if the User sets a different ecoding for GPG he has to set it in
Gajim aswell.

- Handle exceptions inside write() instead of propagating the
    exception
- Add error message to exception
- Add dispatch() method in logger

- Pass EventObj instead of variables
- decrease indent level
- check all conditions inside log_message() not before calling
- fixed bug where gc private messages where not logged with the correct jid

use a class method to remove the resource from JID

use ascii_letters which should be sufficient

Sending Message Refactoring

See merge request !80

- Dont use callbacks, they have no gain in that situation and make the code hard to read
- pass the whole object to a new Event instead of many vars

_build_message_stanza is a better fitting name

- Add a _encrypt_message() and _finished_encrypt() method
- Handle Fallback body text in _on_continue_message() where we build the Stanza

This makes it much easier to read and modify

Various small cleanups, with focus on logger and history window

See merge request !77

Both methods get_conversation_for_date and search_log in the logger
module are related to the loading of conversations and both return a
list of messages from the log. Therefore, it makes sense that both of
them have the same return type.

Remove the named tuple type specific to search_log and convert the
method to return tuples of type Message instead. As a side effect of
this change, search_log now also returns values from the additional_data
column in the log database.

The logger method get_conversation_for_date has previously been
converted to return a list of named tuples. Now pass these tuples on to
the method that actually inserts the conversation's messages into the
textbuffer. Also rename two related methods in the history window:
  -  _add_lines_for_date => _load_conversation
  -  _add_new_line => _add_message

The get_conversation_for_date method in the logger module returns a
list of bare tuples. Knowledge of how to pack and unpack the many
individual components of the tuples is split between the caller and
the callee, making the method hard to maintain and ugly to use.
Therefore, convert the method to return named tuple instead.