[modules] start pimping dependencies

Start working on #940

This replaces
```xml
<depend require="foo|bar" conflict="baz"/>
```
with
```xml
<depends>foo,bar</depends>
<conflicts>baz</conflicts>
```

and now allows to specify OR dependencies with | (pipe) similaro to Debian depends:
```xml
<depends>foo,bar,this|that</depends>
```
which would depend on: foo AND bar AND (this OR that)

conf/modules/digital_cam_i2c.xml

@@ -9,7 +9,7 @@
     <define name="DC_SHOOT_ON_BUTTON_RELEASE" />
     <define name="DC_SHOT_SYNC_SEND" value="TRUE|FALSE" description="send DC_SHOT message when photo was taken (default: TRUE)"/>
   </doc>
-
+  <conflicts>digital_cam,digital_cam_servo,digital_cam_uart</conflicts>
   <header>
     <file name="atmega_i2c_cam_ctrl.h"/>
     <file name="dc.h"/>