Edited IDF for OFFSPEC

Offspec can now find the information associated with slit1,2,3,4.
There was an error in definition of slits in the XML which is now corrected.
As this file was given by an instrument scientist and there are existing system tests for this file there are no more appropriate tests that can be ran for this.
Refs #11806

Code/Mantid/instrument/OFFSPEC_Definition.xml

@@ -34,15 +34,15 @@ name="OFFSPEC" valid-from   ="2012-07-10 22:00:00"
   <!-- LIST OF PHYSICAL COMPONENTS (which the instrument consists of) -->
 
 
-  <component type="slit1">
+  <component name="slit1" type="slit1">
     <location z="-5.6398"/> <!-- From survey,  28/11/2014  -->
      <!-- This log file stores the vertical opening of slit -->
     <parameter name="vertical gap">
       <logfile id="s1vgap" extract-single-value-as="last_value" />
     </parameter>
                   </component>
 
-  <component type="slit2"> 
+  <component name="slit2" type="slit2"> 
     <location z="-0.67045"/> <!-- x=18.1902+4.9693   -->
     <!-- This log file stores the vertical opening of this. Note this
      slit can also be translated in the z. However this info not stored
@@ -52,15 +52,15 @@ name="OFFSPEC" valid-from   ="2012-07-10 22:00:00"
     </parameter> 
   </component>   
 
-  <component type="slit3">  
+  <component name="slit3" type="slit3">  
     <location z="0.6"/> <!-- estimated from MagC position, not accurate   -->
     <!-- This log file stores the vertical opening of slit --> 
     <parameter name="vertical gap">
       <logfile id="s3vgap" extract-single-value-as="last_value" />       
     </parameter>
   </component>   
 
-  <component type="slit4">   
+  <component name="slit4" type="slit4">   
     <location z="2.64"/>     <!-- estimated from MagD position, not accurate   -->
     <!-- This log file stores the vertical opening of slit. Note this slit
      is fixed to the point detector. -->
@@ -73,6 +73,7 @@ name="OFFSPEC" valid-from   ="2012-07-10 22:00:00"
   <type name="slit2"></type>
   <type name="slit3"></type>
   <type name="slit4"></type>
+
   <!-- detector components (including monitors) -->
 
   <component type="monitor1" idlist="monitor1">