Gajim crashes on activating Omemo

[Stuebs]

## Versions
- OS: Ubuntu 19.10
- GTK+ Version: 3.24.12
- PyGObject Version: 3.34.0
- python-nbxmpp Version: 0.6.10
- Gajim Version: 1.1.3

## Traceback
```
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/gajim/plugins/helpers.py", line 114, in wrapper
    result = f(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/gajim/plugins/gui.py", line 201, in installed_plugins_toggled_cb
    app.plugin_manager.activate_plugin(plugin)
  File "/usr/lib/python3/dist-packages/gajim/plugins/helpers.py", line 114, in wrapper
    result = f(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/gajim/plugins/pluginmanager.py", line 453, in activate_plugin
    plugin.activate()
  File "/usr/lib/python3/dist-packages/gajim/./data/plugins/omemo/omemoplugin.py", line 176, in activate
    self.connections[account] = OMEMOConnection(account, self)
  File "/usr/lib/python3/dist-packages/gajim/./data/plugins/omemo/omemo_connection.py", line 48, in __init__
    self.omemo = self.__get_omemo()
  File "/usr/lib/python3/dist-packages/gajim/./data/plugins/omemo/omemo_connection.py", line 97, in __get_omemo
    return OmemoState(self.own_jid, conn, self.account, self)
  File "/usr/lib/python3/dist-packages/gajim/./data/plugins/omemo/omemo/state.py", line 65, in __init__
    self.store = LiteAxolotlStore(db_con)
  File "/usr/lib/python3/dist-packages/gajim/./data/plugins/omemo/omemo/liteaxolotlstore.py", line 57, in __init__
    self._generate_axolotl_keys()
  File "/usr/lib/python3/dist-packages/gajim/./data/plugins/omemo/omemo/liteaxolotlstore.py", line 62, in _generate_axolotl_keys
    preKeys = KeyHelper.generatePreKeys(KeyHelper.getRandomSequence(),
TypeError: getRandomSequence() missing 1 required positional argument: 'max'

```
## Steps to reproduce the problem

- Install gajim and gajim-omemo
- Configure an XMPP/Jabber account
- Open plugin dialog
- Click on checkbox to activate OMEMO
- Bugreport/log appears

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: gajim-omemo 2.6.27-1
ProcVersionSignature: Ubuntu 5.3.0-42.34-generic 5.3.18
Uname: Linux 5.3.0-42-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu8.5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Mar 11 14:16:21 2020
InstallationDate: Installed on 2019-05-07 (309 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: gajim-omemo
UpgradeStatus: Upgraded to eoan on 2020-03-06 (5 days ago)

[Stuebs (stuebs)]

it seems that gajim-omemo requires python3-axolotl version 0.2.2.
```
apt show python3-axolotl
Package: python3-axolotl
Version: 0.2.3-3
```

[Muelli (ubuntu-bugs-auftrags-killer)]

upstream: https://dev.gajim.org/gajim/gajim-plugins/issues/462

probably the same issue here, but manually filed: https://bugs.launchpad.net/ubuntu/+bug/1853449