nav: fix double jumping when bot gets stuck

bot: restore bot difficulty levels (ref #729)
bot: probably fix freezetime accident shooting (ref #729)
build: use noexecstack when building library
refactor: rework some old code and remove unnecessary things

inc/manager.h

@@ -59,6 +59,8 @@ private:
    edict_t *m_killerEntity {}; // killer entity for bots
    BotTeamData  m_teamData[kGameTeamNum] {}; // teams shared data
 
+   CountdownTimer m_holdQuotaManagementTimer {}; // prevent from running quota management for some time
+
 protected:
    BotCreateResult create (StringRef name, int difficulty, int personality, int team, int skin);