1. A method for multi-layered customization of web-based applications, the method comprising: receiving, at one or more computer systems, a request generated by a client device for a user interface of an web-based application; determining, by the one or more computer systems, first metadata associated with a user of the client device, wherein the first metadata comprises a first layer in a hierarchical set of a plurality of configuration layers for the web-based application, the first metadata comprising a first setting for each of one or more user interface elements of the web-based application, wherein the first setting of a user interface element comprises a value specified by the user of the client device indicating a procedure of the web-based application that receives input from the user interface element; determining, by the one or more computer systems, second metadata provided by a supervisor of the user of the client device, wherein the second metadata comprises a second layer in the hierarchical set of the plurality of configuration layers for the web-based application, the second metadata comprising a second setting for each of the one or more user interface elements of the web-based application, wherein the second setting of a user interface element comprises a value specified by the supervisor indicating a procedure of the web-based application that receives input from the user interface element; receiving, at the one or more computer systems, a page definition for the user interface of the web-based application, wherein the page definition comprises metadata defining a plurality of user interface elements of the user interface; determining, by the computer system, a setting for at least one of the plurality of user interface elements based on the first metadata, the second metadata, and the page definition, wherein the determined setting for the user interface element overrides any settings in the second metadata and the page definition without modifying design of the user interface; and sending, by the one or more computer systems, an instance of the user interface of the application to the client device, the instance of the user interface generated based on the determined setting.