Adjust Conjurer and Air Elementalist spellbooks

Replace Battlesphere in the book of Conjurations with Force Lance, as
Battlephere tended to overwhelm use of the book's other interesting spells like
Fulminant Prism, and Force Lance potentially has some interaction with knocking
enemies back into the Prism's range, for example. Also replace the newly-added
Summon Lightning Spire in the book of Air with Airstrike, since again the
summon spell would be likely to become the major focus of the book. Airstrike's
relatively low damage means the existing spells such as Static Discharge and
Lightning Bolt should still be important.

crawl-ref/source/book-data.h

@@ -16,8 +16,8 @@ static const vector<spell_type> spellbook_templates[] =
     SPELL_SEARING_RAY,
     SPELL_DAZZLING_SPRAY,
     SPELL_FULMINANT_PRISM,
+    SPELL_FORCE_LANCE,
     SPELL_ISKENDERUNS_MYSTIC_BLAST,
-    SPELL_BATTLESPHERE,
 },
 
 {   // Book of Flames
@@ -185,12 +185,12 @@ static const vector<spell_type> spellbook_templates[] =
     SPELL_SHOCK,
     SPELL_SWIFTNESS,
     SPELL_DISCHARGE,
-    SPELL_SUMMON_LIGHTNING_SPIRE,
+    SPELL_AIRSTRIKE,
     SPELL_LIGHTNING_BOLT,
 },
 
 {   // Book of the Sky
-    SPELL_AIRSTRIKE,
+    SPELL_SUMMON_LIGHTNING_SPIRE,
     SPELL_SILENCE,
     SPELL_DEFLECT_MISSILES,
     SPELL_CONJURE_BALL_LIGHTNING,
@@ -264,8 +264,7 @@ static const vector<spell_type> spellbook_templates[] =
 #endif
 
 {   // Book of Power
-    SPELL_FULMINANT_PRISM,
-    SPELL_ISKENDERUNS_MYSTIC_BLAST,
+    SPELL_BATTLESPHERE,
     SPELL_VENOM_BOLT,
     SPELL_BOLT_OF_MAGMA,
     SPELL_IRON_SHOT,