added possibility to add annotations to graphs (#16)
added possibility to add annotations to graphs (#16), now with Annotatino classes
added annotation classes to Makefile.am
added annotation table in create_table and put functionality for annotations
formatted code
Revert "formatted code"

This reverts commit ee682a1e2ba5aa84571c60b48aa75a87acecebbf.
formatted relevant code
refactored metrics form tag edit elements

introduced class TagsPanel to encapsulate the form elements and logic
for manipulating tags as a preparation to reuse the panel for the
annotations tags manipulation
introduced AnnotationsForm to manipulate the tags that should be used as filter for annotations
added query build to AnnotationsForm

added query build to AnnotationsForm
implemented tag retrieval in TagsPanel
changed TagsPanel#getTags() to allow for duplicate keys and added logic to create graph from separate query parameters

getTags() now returns a String[][] with tag keys and values.
added query parameter "a" to define tag filters for annotations
removed 'tsdb-annotation' table to store annotation values

annotations are now being stored in the 'tsdb' table together with
metric values.
implemented UI changes to define arithmetic expressions

added an extra text field with auto-suggest functionality for
arithmetic expressions; the auto-suggest works with already selected
metrics from the metrics form
added ANTLR grammatic and calculator class to interpret arithmetic expressions

the parser/lexer/tree walker are generated by ANTLR at build time, so
they are not checked in
added ID to query to be able to identify a query object uniquely after is has been created

this identification is needed for the arithmetic expressions to map
query results to operators in an arithmetic expression
refactored GraphHandler to be more readable and consistent and to support the plotting of arithmetic expression results

introduction of several small helper methods to get doGraph() small
enough to be readable
fixed NPE in ArithmeticExpressionCalculator: empty expressions are ignored
removed 'tsdb-annotation' table from "create-tables.sh" script
removed NPE in GWT code when working with the JSON result for a query (possibly a consequence of the annotations being stored inside the 'tsdb' table)
fixed NPE in GraphHandler for missing "e" URL parameter

when the "e" URL parameter is not being added to the URL (e.g. for legacy graph URLs), then a NullPointerException occured. This has been fixed.