Allow loading external plugins called "Enhancers" that as the name suggests,
enhance Clapper library capabilities.
Currently implemented is a "ClapperExtractable" interface meant to extract
an actual media that GStreamer can later play from an initial input URI.
Additionally, an internal GStreamer elements that work with it are ported/moved
here from "gtuber" library that this functionality replaces.
* New translations clapper-gtk.pot (Hindi)
* New translations clapper-app.pot (Russian)
* New translations clapper-gtk.pot (Czech)
* New translations clapper-gtk.pot (Persian)
* New translations clapper-gtk.pot (Norwegian)
Since missing plugin string is translated, word describing its type
(e.g. Decoder) might come before plugin name itself, so we need to
check whole text to find substring instead of checking only prefix.
Fixes#477
Do not require applications to import GStreamer and their devs to learn its
basics just to set this single element. Similarly as ClapperGtkVideo sets
"clappersink" during construction, it can also set "scaletempo" as this is
the most common choice for an audio filter.
Elements can still be changed like before if desired by setting corresponding
player properties.
Allow creating item with a previously downloaded cache file.
When set, file at location will be tried to be loaded first.
If this fails, URI will be used as normal.
Short video might be fully downloaded before playback starts.
This prevents us from emitting "download-complete" signal with
corresponding media item when download cache is enabled.
Check if we have pending item, as this will be the item downloaded
in such case (before it becomes playing item).
A possibility exists that something else keeps a reference to the player
even after video is disposed. In this case signals from the player would
not be disconnected.
We have to disconnect them manually here to ensure their callbacks will
not be used after disposal.
When a new window is created, apply all current values to it (volume, speed,
set GStreamer elements, etc.). It would not be the best experience when user
opens a new window, plays something and 100% volume is used in it.
Instead of running into warnings or other problems when user
specifies an out of range value for command line option, just
clamp them to nearest allowed one.
Now that we are using both local and global command line vfuncs, we
can just get and apply options in them and free values later.
This avoids having options global and static.
