freeze requirements and change pip install command

prepare.sh

@@ -1,2 +1,4 @@
+#!/bin/sh
+
 sudo apt-get install build-essential python-dev python-pip
-sudo pip install Flask Flask-Session Flask-SQLAlchemy Flask-Mail apscheduler passlib
+pip install -r requirements.txt

requirements.txt

@@ -0,0 +1,8 @@
+APScheduler==3.0.1
+Flask==0.10.1
+Flask-Mail==0.9.1
+Flask-SQLAlchemy==2.0
+Flask-Session==0.1.1
+SQLAlchemy==0.9.8
+passlib==1.6.2
+six==1.8.0