more screenshots and remove some redundant references to README's

apps.json

@@ -394,6 +394,7 @@
     "version": "0.02",
     "description": "inspired by The Matrix, a clock of the same style",
     "icon": "matrixclock.png",
+    "screenshots": [{"url":"screenshot_matrix.png"}],
     "type": "clock",
     "tags": "clock",
     "supports": ["BANGLEJS","BANGLEJS2"],
@@ -448,7 +449,6 @@
     "type": "clock",
     "tags": "clock",
     "supports": ["BANGLEJS","BANGLEJS2"],
-    "readme": "README.md",
     "allow_emulator": true,
     "storage": [
       {"name":"aclock.app.js","url":"clock-analog.js"},
@@ -512,6 +512,7 @@
     "version": "0.03",
     "description": "Retro asteroids game",
     "icon": "asteroids.png",
+    "screenshots": [{"url":"screenshot_asteroids.png"}],
     "tags": "game",
     "supports": ["BANGLEJS","BANGLEJS2"],
     "allow_emulator": true,
@@ -552,6 +553,7 @@
     "version": "0.04",
     "description": "Simple compass that points North",
     "icon": "compass.png",
+    "screenshots": [{"url":"screenshot_compass.png"}],
     "tags": "tool,outdoors",
     "supports": ["BANGLEJS","BANGLEJS2"],
     "storage": [
@@ -3571,7 +3573,6 @@
     "type": "clock",
     "tags": "clock",
     "supports": ["BANGLEJS","BANGLEJS2"],
-    "readme": "README.md",
     "storage": [
       {"name":"simplest.app.js","url":"app.js"},
       {"name":"simplest.img","url":"icon.js","evaluate":true}