CorePlugin: Use static VariableManager functions where appropriate

Change-Id: Ie3d34a829522e15b2a56c0fcc696e60163a9be32
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
EditorManager: Use static pattern, adjust surrounding code

Change-Id: I3255a0150cd9a730336456c5a9f986eb74fefbff
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
EditorManager: Use interface directly instead of going through ICore

In the majority of cases we were doing that anyways, having two
ways is just needlessly confusing.

Change-Id: Ied362a702c23beee528368d74df1f2aabe5807f8
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Core: Remove deprecated accessors

Also adjust user code.

Change-Id: I60935942a7012e6a0d6091ffbc89d69289366e35
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Core: Force use of static DocumentManager interface

Change-Id: Ieb2c0ecd3d34a3aad653c6eb5b00bc20d2c61986
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Compile fix

Change-Id: I522fa14be958284fb8ed3ff4626a31b8ee575546
Reviewed-by: hjk <hjk121@nokiamail.com>