build: Prepares for 0.1.29 development cycle which will release 0.2.0
Adds a EvdIoStreamGroup 'group' member to EvdIoStream

Purpose is to migrate the 'group' member of EvdConnection down in the object
hierarchy to EvdIoStream.

Also adds:
- the corresponding getter and setter methods,
- a read/write 'group' property,
- a 'group-changed' signal,
- a 'group_changed' virtual method.
Adds new signal 'close' to EvdIoStream

Purpose is to move the 'close' signal of EvdConnection down in the object
hierarchy to EvdIoStream.
Fails EvdTransport::open() method if not implemented
Makes EvdIoStreamGroup to watch 'close' signal of streams and auto-remove them

This implies a significant change in how streams and groups are handled. Before,
specialized IO stream groups like EvdService and EvdConnectionPool were
responsible for removing the streams when the were closed. Now the base IO
stream group handles that automatically by default.

Stream groups can still override the add() or remove() virtual methods to
implement a different logic, and can chain up to EvdIoStreamGroup's base
methods to use this new stream auto-tracking feature.

This change also implies that EvdIoStreamGroup now maintains a GList with its
streams to be able to disconnect from 'close' signal when the group is disposed.
Fully removes the 'group' member from EvdConnection

The group member has been moved to EvdIoStream.

The 'group' property, the 'group-changed' signal, and the corresponding getter
and setter methods were also removed.
Removes 'close' signal from EvdConnection

The signal has been moved to EvdIoStream.
Updates EvdWebService to use get_group() method from EvdIoStream

instead of EvdConnection.
Updates EvdService to remove tracking of connection closure

This is now handled in EvdIoStreamGroup.

The connection_closed() virtual method is also removed.
Improves object reference tracking of socket listeners in EvdService
Updates EvdConnectionPool to use get_group() method from EvdIoStream

instead of EvdConnection.
Keeps a temporary reference to EvdIoStream while setting its group
Uses dispose() instead of finalize() to unref object members in EvdIoStream
Removes an EvdIoStream from its group when closed or destroyed
Removes IO stream tracking in EvdIoStreamGroup

This turned out not to be such a good idea. Maintaining a GList of streams
implies iterating the list every time an element is removed from the group.
This is not efficient performance-wise.

Now, it is the EvdIoStream object the one responsible to remove itself from
its group (if any) when closed or destroyed.
Updates EvdConnectionPool to use add/remove methods from EvdIoStreamGroup

to handle its pooled connections.
Makes EvdService use add() virtual method from EvdIoStreamGroup

for new connections, instead of calling its own.
Adds new unit test for EvdIoStream grouping API
Removes EvdServiceValidate and makes EvdService use EvdValidateEnum
Adds new signal 'validate-tls-connection' to EvdService

and renames validate_connection() signal prototype to
signal_validate_connection(), for consistency.