added tab stuff for derivatives
Merge branch 'master' of https://github.com/mfulgencio/EducationalApp

Conflicts:
	MathPath/AndroidManifest.xml
	MathPath/res/layout/limits_tabs_layout.xml
	MathPath/src/com/example/educationalapp/DerivativeTabs.java
	MathPath/src/com/example/educationalapp/LimitsTabs.java
	MathPath/src/com/example/educationalapp/Tabs.java
	MathPath/src/com/example/educationalapp/Topics.java