[timeline] Create markers hash tables on demand
[timeline] Create markers hash tables on demand

Since not every timeline will have markers it's unfair to make
all of them crete two empty hash tables (with a preallocated
fixed size).

This commit moves the responsibility of creating the hash tables
to the marker API itself, and adds the relative checks.

heysion/clutter-clone,GNOME/clutter,djdeath/clutter-multithreaded,nobled/clutter,collects/clutter,tardyp/clutter,ebassi/clutter,tardyp/clutter,jigpu/clutter,djdeath/clutter-multithreaded,kerrickstaley/clutter-vala,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,djdeath/clutter,djdeath/clutter,djdeath/clutter-android,GNOME/clutter,spatulasnout/clutter,dlespiau/clutter,djdeath/clutter,GNOME/clutter,rkudiyarov/clutter_osx,kerrickstaley/clutter-vala,Distrotech/clutter,heysion/clutter-clone,djdeath/clutter,rkudiyarov/clutter_osx,ebassi/clutter,jigpu/clutter,rkudiyarov/clutter_osx,nobled/clutter,djdeath/clutter-android,collects/clutter,collects/clutter,dlespiau/clutter,GNOME/clutter,collects/clutter,spatulasnout/clutter,dlespiau/clutter,djdeath/clutter-android,ebassi/clutter,djdeath/clutter-android,jigpu/clutter,jigpu/clutter,ebassi/clutter,Distrotech/clutter,jigpu/clutter,Distrotech/clutter,kerrickstaley/clutter-vala,heysion/clutter-clone,Distrotech/clutter,GNOME/clutter,djdeath/clutter,heysion/clutter-clone,spatulasnout/clutter,Distrotech/clutter,jigpu/clutter,nobled/clutter,Distrotech/clutter,djdeath/clutter-multithreaded,spatulasnout/clutter,djdeath/clutter-android,djdeath/clutter,tardyp/clutter,rkudiyarov/clutter_osx,ebassi/clutter,heysion/clutter-clone,spatulasnout/clutter,collects/clutter