Replacing existing browser tree node png icons with the svg icons. Made

it compatible with the pgAdmin 4 color combination.

TODO::
Icons for the following nodes are in PNG format.
- Domain Constraint (Only the invalid icon)
- pgAgent Job Steps
- Green Plum database server
- Server (Only server.png, which is used in the create/edit dialog)

web/pgadmin/browser/server_groups/servers/tablespaces/static/img/coll-tablespace.svg

@@ -0,0 +1 @@
+<svg id="Layer_1" data-name="Layer 1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><defs><style>.cls-1,.cls-2{fill:#def4fd;}.cls-1{stroke:#717f8e;}.cls-1,.cls-2,.cls-3{stroke-linecap:round;stroke-linejoin:round;stroke-width:0.75px;}.cls-2,.cls-3{stroke:#2980b9;}.cls-3{fill:#c5e5fc;}</style></defs><title>coll-tablespace</title><polygon class="cls-1" points="4.5 4.5 0.5 4.5 0.5 2.5 3.63 2.5 4.5 3.12 4.5 4.5"/><rect class="cls-1" x="0.5" y="4.5" width="9" height="5"/><rect class="cls-2" x="2.5" y="8.5" width="9" height="5"/><polygon class="cls-3" points="6.5 8.5 2.5 8.5 2.5 6.5 5.63 6.5 6.5 7.12 6.5 8.5"/></svg>

web/pgadmin/browser/server_groups/servers/tablespaces/static/img/tablespace.svg

@@ -0,0 +1 @@
+<svg id="Layer_1" data-name="Layer 1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><defs><style>.cls-1{fill:#def4fd;stroke:#2980b9;stroke-linecap:round;stroke-linejoin:round;stroke-width:0.75px;}</style></defs><title>tablespace</title><rect class="cls-1" x="0.5" y="5.75" width="10" height="6.5"/><polygon class="cls-1" points="6 5.75 0.5 5.75 0.5 3.75 4.69 3.75 6 4.68 6 5.75"/></svg>