menu, icon buttons, & constraints added (but not perfect yet)
added ability to select subexpressions
testing with IgnoreMe
ignore this change - just testing something
statements-isolated, theorem panel
add annotations

I've added a boatload of @Override and @SuppressWarnings("serial")
annotations. This commit shouldn't change how things work; it just gets
rid of warnings in Eclipse.
remove unused imports

Shouldn't change how anything works; just makes errors in Eclipse go
away.
remove unused variables

The Tester class (and the instance of it in the MainWindow) get an
@SuppressWarnings("unused") notation instead of removal.
an operator's name is accessed through toString()

Just because operator names are final doesn't mean we can't encapsulate
them!
Merge branch 'master' into selectable-subexpressions

Conflicts:
	src/Expression.java
	src/ExpressionListCellRenderer.java
	src/ExpressionSelectionDialog.java
	src/MainWindow.java
	src/Operator.java
	src/OperatorExpression.java
	src/OperatorSpec.java
	src/Operators.java
	src/PCircle.java
	src/PLine.java
	src/PPoint.java
	src/PRay.java
	src/PSegment.java
	src/SketchCanvas.java
	src/Statement.java
	src/VariableExpression.java
Post-merge Cleanup

Image files have been moved from ./src/res/ to ./res/images/. The
location of the image files can be configured in the settings file
(./settings.txt).
Slight improvement in allDependentsExist()

The search now returns early if any dependent fails to exist. The
double-recursion isn't quite as bad as it looks because ||
short-circuits: If a dependent doesn't exist, none of its dependents are
checked. The only better way I could think of to do this would involve
keeping a list of all the drawables we have checked, to avoid checking
any one twice.
Merge in recent changes in master

Many of these changes, by the way, were inspired by comments in this
branch.
Merge branch 'selectable-subexpressions'

Conflicts:
	src/Expression.java
	src/MainWindow.java
	src/Operator.java
	src/OperatorExpression.java
	src/VariableExpression.java