Do not ignore case for ace jump mode
Bind a key for helm-imenu
Rebind some basic keys
Fix current position is not preserved

When using semantic-ia-fast-jump or semantic-analyze-proto-impl-toggle,
the current position is not preserved before jumping around. Therefore
we cannot jump back correct when using back-button-global-forward and
back-button-global-backward.

We fix it by replacing push-mark. Also we do not need to advice
ace-jump-mode anymore.