Introduce specific getters and setters for database

To retreive a parameter's value from the database, we are using:

dao.get_config("remote_token")  # string or None
dao.get_config("ssl_verify", "1") != "0"  # bool

 
As we saw with NXDRIVE-1490, we also have:

dao.get_config("ssl_verify", default=True)

 
Which is not intuitive: asking for a boolean as the default value is suggesting but the database stores only integers returned as strings.

So the prevent such errors/misuses, we should introduce specific getters:

dao.get_int("param", default=0)
dao.get_bool("param", default=False)

We keep dao.get_config() to retreive other values.

And so for setters:

dao.store_int("param", 42)
dao.store_bool("param", True)

We keep dao.update_config() to store other values.