fix selects: use child scope inside the directive

Before, if we wanted to use a scope method inside the
"lx-select-selected" or "lx-select-choices", we couldn't because the
directive scope was isolated.
By using a child scope, we keep access to all of the data from the
parent scope. Making this, we now use "ng-model" to manage the model as
the two-ways binding is only doable in an isolated scope.

BROKEN:
selects now use "ng-model" instead of "model"
fix tooltip: remove element on scope destroy

Sometimes the tooltip was still visible in the screen even after a page
change. By deleting the tooltip's element from the DOM when the scope is
destroyed, we ensure that the tooltip don't stay visible.
fix dropdown: remove element on scope destroy

Sometimes the dropdown was still visible in the screen even after a page
change. By deleting the dropdown's element from the DOM when the scope
is destroyed, we ensure that the dropdown don't stay visible.
chore changelog: release v0.2.25
fix selects: add default scope values

By managing the directive with a child scope, a bug was introduced as a
non-defined function in the directive could be defined in the parent
scope with the same name. Adding default value in the directive scope
fixed the problem.
chore changelog: release v0.2.26
fix date-picker: watch the scope to handle async binding
fix date-picker: move isDefined checking to controller