HttT: makings some events more translation-friendly

The fiters restrict the events for exactly one particular unit.
Filtering the messages also by the unit id unstead of the generic "unit" variable
shows in the translation file who speaks the message - instead of the generic "unit"
shown otherwise.
[ci skip]

data/campaigns/Heir_To_The_Throne/scenarios/01_The_Elves_Besieged.cfg

@@ -335,7 +335,7 @@
             id=Konrad
         [/filter]
         [message]
-            speaker=unit
+            speaker=Konrad
             message= _ "Very well, we have made it this far! But where do we go next?"
         [/message]
         [message]
@@ -343,7 +343,7 @@
             message= _ "We must travel north, and try to make it to the Isle of Alduin. Hopefully we will find refuge there."
         [/message]
         [message]
-            speaker=unit
+            speaker=Konrad
             message= _ "Of course you are right, Delfador. But what will become of the elves here?"
         [/message]
         [message]
@@ -367,7 +367,7 @@
             id=Konrad
         [/filter]
         [message]
-            speaker=unit
+            speaker=Konrad
             {KONRAD_VARIATION_ELF concerned}
             message= _ "I... I don’t think I can make it anymore."
         [/message]
@@ -376,7 +376,7 @@
             message= _ "Prince... you must keep fighting! Nooooooo!"
         [/message]
         [message]
-            speaker=unit
+            speaker=Konrad
             {KONRAD_VARIATION_ELF concerned}
             message= _ "It is over. I am doomed..."
         [/message]
@@ -391,7 +391,7 @@
             id=Delfador
         [/filter]
         [message]
-            speaker=unit
+            speaker=Delfador
             message= _ "I have... have failed in my duty to protect the prince! I am defeated."
         [/message]
         [message]
@@ -400,7 +400,7 @@
             message= _ "Don’t die, Delfador! Please, you have to stay alive!"
         [/message]
         [message]
-            speaker=unit
+            speaker=Delfador
             message= _ "Ugh!"
         [/message]
         [endlevel]
@@ -434,7 +434,7 @@
             id=Delfador
         [/filter_second]
         [message]
-            speaker=second_unit
+            speaker=Delfador
             message= _ "Only the foolish oppose me!"
         [/message]
     [/event]

data/campaigns/Heir_To_The_Throne/scenarios/05b_Isle_of_the_Damned.cfg

@@ -443,7 +443,7 @@
         [/filter]
 
         [message]
-            speaker=unit
+            speaker=Moremirmu
             message= _ "Fight on against the undead without me, friends!"
         [/message]
         [set_variable]